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The ability to manipulate the refractive index is a fundamental principle underlying numerous photonic devices. Various techniques exist to modify the refractive index across diverse materials, making performance comparison far from straightforward. In evaluating these methods, power consumption emerges as a key performance characteristic, alongside bandwidth and footprint. Here a comprehensive comparison of the energy and power requirements for the most well‐known index change schemes is undertaken. The findings reveal that while the energy per volume for index change remains within one or two orders of magnitude across different techniques and materials, the power consumption required to achieve switching, 100% modulation, or 100% frequency conversion can differ significantly, spanning many orders of magnitude. As it turns out, the material used has less influence on power reduction than the specific resonant or traveling wave scheme employed to enhance the interaction time between light and matter. Though this work is not intended to serve as a design guide, it does establish the limitations and trade‐offs involved in index modulation, thus providing valuable insights for photonics practitioners. [ABSTRACT FROM AUTHOR]

Fully CMOS-compatible photonic memory holding devices hold a potential in the development of ultrafast artificial neural networks. Leveraging the benefits of photonics such as high-bandwidth, low latencies, low-energy interconnect, and high speed, they can overcome the existing limits of electronic processing. To satisfy all these requirements, a photonic platform is proposed that combines low-loss nitride-rich silicon as a guide and low-loss transparent conductive oxides as an active material that can provide high nonlinearity and bistability under both electrical and optical signals. [ABSTRACT FROM AUTHOR]

The performance of a recently proposed integrated graphene-bolometric photodetector is assessed. The responsivity of hundreds of A/W and speed on the scale of hundreds of GHz are predicted. The impressive performance is attributed to the small length over which the energy is absorbed by graphene. The short length leads to a highly enhanced energy density, which causes the increase of the electron temperature in graphene. The model has been validated against recently published experimental results from high-speed graphene photodetectors and found to be in good agreement. [ABSTRACT FROM AUTHOR]

High refractive index dielectrics enable nanoscale integration of optical components with practically no absorption loss. Hence, high index dielectrics are promising for many emerging applications in nanophotonics. However, the lack of a complete library of high index dielectric materials poses a significant challenge to understanding the full potential for dielectric nanophotonics. Currently, it is assumed that the absorption edge and the sub‐bandgap refractive index of a semiconductor exhibit a rigid trade‐off, popularly known as the Moss rule. Thus, the Moss rule appears to set an upper limit on the refractive index of a dielectric for a given operating wavelength. However, there are many dielectric materials that surpass the Moss rule, referred to here as super‐Mossian dielectrics. Here, the general features of super‐Mossian dielectrics and their physical origin are discussed to facilitate the search for high index dielectrics. As an example, iron pyrite, an outstanding super‐Mossian material with index nearly 40% higher than the Moss rule prediction, is developed. The local dielectric resonances in iron pyrite nanoresonators are experimentally observed, and the impact of super‐Mossian materials on nanophotonics is demonstrated. [ABSTRACT FROM AUTHOR]

Permanent dipole moments of electronic states in non-centrosymmetric materials play a pivotal role in many phenomena. Correctly evaluating them presents an arduous task and usually requires full knowledge of the band structure as well as understanding the intricate concepts of Berry curvature. Here, we show that in a few cases (e.g., zinc blende and wurtzite) a rather facile first-principle analytical derivation of the permanent dipole moments using L'Hôpital's rule can be performed, and the values and dispersion of these dipoles near high symmetry points can be found using just a couple of widely available material parameters. The results will hopefully contribute to better understanding of shift currents, optical rectification, and other electro-optical phenomena. [ABSTRACT FROM AUTHOR]

As lasers get more and more miniaturized and their dimensions become comparable to the wavelength, two interconnected phenomena take place: the fraction of spontaneous radiation going into a specific laser mode (β‐factor) increases and can ultimately reach unity, while the radiative lifetime gets shortened by the Purcell factor Fp. Often it is assumed that an increase of these two factors, along with the quality factor (Q‐factor), almost invariably causes reduction of the lasing threshold. This assumption is tested on various photonic and plasmonic lasers, demonstrating that, while there is obvious correlation between the aforementioned factors and the laser threshold, the dependence is far from being straightforward and omnipresent. Depending on specific laser material and geometry, the threshold can decrease, increase, or stay unchanged when β‐factor, Q‐factor, and Fp increase. For the most part, the reduction of threshold is achieved simply by reducing the laser volume and this volume reduction can concurrently cause the increase in β‐factor and/or Purcell factor, but it would be imprudent to say that the increase in either of these factors is the cause of the threshold reduction. [ABSTRACT FROM AUTHOR]

Novel materials, with enhanced light–matter interaction capabilities, play an essential role in achieving the lofty goals of nonlinear optics. Recently, epsilon‐near‐zero (ENZ) media have emerged as a promising candidate to enable the enhancement of several nonlinear processes including refractive index modulation and harmonic generation. Here, the optical nonlinearity of ENZ media is analyzed to clarify the commonalities with other nonlinear media and its unique properties. Transparent conducting oxides as the family of ENZ media with near‐zero permittivity in the near‐infrared (telecom) band are focused on. The instantaneous and delayed nonlinearities are investigated. By identifying their common origin from the band nonparabolicity, it is shown that their relative strength is entirely determined by a ratio of the energy and momentum relaxation (or dephasing) times. Using this framework, ENZ materials are compared against the many promising nonlinear media that are investigated in literature and show that while ENZ materials do not radically outpace the strength of traditional materials in either the fast or slow nonlinearity, they pack key advantages such as an ideal response time, intrinsic slow light enhancement, and broadband nature in a compact platform making them a valuable tool for ultrafast photonics applications for decades to come. [ABSTRACT FROM AUTHOR]

An analytical expression for the maximum potential bandwidth of the frequency modulated comb naturally occurring in free running quantum cascade lasers (QCLs) has been derived. The maximum bandwidth is not as wide as the one attainable in passively mode locked lasers, but wider than that in the actively mode locked ones. The bandwidth is shown to critically depend on the flatness of the gain spectrum and the cavity length and less so on pump current. The results firmly establish that the performance of QCL frequency combs can be on par with combs generated by other means. [ABSTRACT FROM AUTHOR]

A number of methods for improvement of the efficiency of laser cooling in semiconductors are suggested and analyzed theoretically. It is shown that by combining band gap engineering in the electronic domain and photonic band gap engineering in the optical domain, one can attain an enhancement in refrigeration efficiency provided the nonradiative efficiency is not drastically affected. [ABSTRACT FROM AUTHOR]

Design results aimed at achieving tunable high-temperature operation in the 3–5 μm atmospheric transmission window are presented for the intersubband Raman lasers based on GaN/AlGaN coupled quantum wells. The ultrafast longitudinal-optical-phonon (LO-phonon) scattering in GaN/AlGaN quantum wells (QWs) can be used for the rapid depopulation of the lower laser state, while the large LO-phonon energies (∼90 meV) allow for a design to minimize the thermal population of the lower laser state, and are therefore beneficial for obtaining high-temperature operation. The Raman gain is proportional to the difference between the virtual lifetime of the upper laser state and the effective lifetime of the lower laser state instead of the real lifetimes. The advantage is that these lifetimes can be tuned with the detuning of the pump photon energy from the subband energy separation. At a fixed pumping wavelength of 2.7 μm, the tuning range of 3.6–5.2 μm is predicted with a moderate Raman gain of at least 100/cm as the electric field is varied. Furthermore, the output power of this laser is unlikely to saturate because of the intrinsically short intersubband lifetimes in the GaN-based QWs. [ABSTRACT FROM AUTHOR]

Proposes a type of three-terminal tunneling device with gating action provided by the external field inducing the changes in the symmetry of electron wave functions. Structure and calculation of the tunneling device; Results and discussion; Conclusion.

For many applications, optical frequency combs (OFCs) require a high degree of temporal coherence (narrow linewidth). Commonly, OFCs are generated in nonlinear media from a monochromatic narrow linewidth laser source or from a mode-locked laser pulse, but in all the important mid-infrared (MIR) and terahertz (THz) regions of the spectrum, OFCs can be generated intrinsically by free-running quantum cascade lasers (QCLs) with high efficiency. These combs do not look like conventional OFCs as the phases of each mode are different, and in the temporal domain, OFCs are a seemingly random combination of amplitude- and phase-modulated signals rather than a short pulse. Despite this "pseudo-randomness," the experimental evidence suggests that the linewidth of a QCL OFC is just as narrow as that of a QCL operating in a single mode. While universally acknowledged, this observation is seemingly not fully understood. In this work, we explicate this fact by deriving the expression for the Schawlow-Townes linewidth of QCL OFCs and offer a transparent physical interpretation based on the orthogonality of laser modes, indicating that despite their very different temporal profiles, MIR and THz QCL OFCs are just as good for most applications as any other OFCs. [ABSTRACT FROM AUTHOR]

Investigates surface-emitting second-harmonic generation in niobate waveguides and in semiconductor multilayers and asymmetric quantum-well domain structures. Comparison of results with those of a Gaussian fundamental phase; Introduction of saturation intensity to quantify the saturation regime.

The article examines a study which analyzes the nonlinear properties of graphene using general qualitative analysis method. Topics discussed include the high-frequency response of graphene, the nonlinear index for the interband transitions, and the nonlinearities of graphene which is strong at low electron densities.

Noble metals that currently dominate the fields of plasmonics and metamaterials suffer from large ohmic losses. Some of the new plasmonic materials, such as doped oxides and nitrides, have smaller material loss, and using them in place of metals carries the promise of reduced-loss plasmonic and metamaterial structures, with sharper resonances and higher field concentrations. This promise is put to a rigorous analytical test in this work, which reveals that having low material loss is not sufficient to have reduced modal loss in plasmonic structures. To reduce the modal loss, it is absolutely necessary for the plasma frequency to be significantly higher than the operational frequency. Using examples of nanoparticle plasmons and gap plasmons one comes to the conclusion that, even in the mid-infrared spectrum, metals continue to hold an advantage over alternative media when it comes to propagation distances and field enhancements. Of course, the new materials still have an application niche where high absorption loss is beneficial, e.g. in medicine and thermal photovoltaics. [ABSTRACT FROM AUTHOR]

Presents a study that considered two-photon transitions from the confined states to the continuum in the semiconductor quantum wells and superlattices. Experimental details; Results of the study; Conclusion.

Presents information on a study which proposed a tunable source of the far-infrared radiation based on intersubband electronic scattering in semiconductor quantum wells. Estimation of the gain and threshold of the proposed Raman oscillator; Rate equations for the population densities.

Longitudinal optical (LO) phonons in GaN generated in the channel of high electron mobility transistors (HEMT) are shown to undergo nearly elastic scattering via collisions with hot electrons. The net result of these collisions is the diffusion of LO phonons in the Brillouin zone causing reduction of phonon and electron temperatures. This previously unexplored diffusion mechanism explicates how an increase in electron density causes reduction of the apparent lifetime of LO phonons, obtained from the time resolved Raman studies and microwave noise measurements, while the actual decay rate of the LO phonons remains unaffected by the carrier density. Therefore, the saturation velocity in GaN HEMT steadily declines with increased carrier density, in a qualitative agreement with experimental results. [ABSTRACT FROM AUTHOR]

The author presents his views on dealing with the loss in plasmonics and metamaterials (P&M). Topics discussed include research on P&M research to manipulate the electromagnetic field on the subwavelength scale for achieving linear and nonlinear optical processes, selection of silver and gold as they have low rate of scattering of free electrons in them and strategies for loss mitigation such as use of highly doped semiconductors instead of metals and polar dielectrics.

Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work, we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling. [ABSTRACT FROM AUTHOR]

Electrically pumped subwavelength plasmonic lasers (spasers) have attracted significant interest in recent years, but their properties are still not well understood, especially in comparison to the ubiquitous all-dielectric semiconductor microlasers (vertical-cavity surface-emitting lasers, VCSELs). Our theoretical analysis reveals that, from the fundamental physics point of view, a spaser does not differ from a semiconductor laser, as most of the energy is contained in the oscillations of electrons (free versus bound) and not in the electromagnetic field. At the same time, due to large losses in the metal, the technical characteristics of a spaser differ significantly from the VCSEL in that the spaser has at least three orders of magnitude higher threshold current density, four to five orders of magnitude wider linewidth, and a speed that is only a few times higher than in a VCSEL or an incoherent surface-plasmon-emitting diode. These results should assist researchers in making an informed choice of emitters for various particular optoelectronic applications. [ABSTRACT FROM AUTHOR]

Abstract: A potentially high throughput waveguide mode multiplexer/demultiplexer (MUX/DEMUX) exemplified by two cascaded Y-junctions is shown to be capable of efficiently transforming modes from single mode waveguides into a two-dimensional set of the orthogonal ones in a multi-mode waveguide, and back. The design parameters of the cascade and the mode transformations are found by accurate beam-propagation modeling for possible realization with optical polymers. The proposed MUX/DEMUX can enable multifold increase of the data rates of multimode links used in datacom and optical computer communications. [Copyright &y& Elsevier]

We describe a simple yet rigorous theoretical model capable of analytical estimation of plasmonic field enhancement in complex metal structures. We show that one can treat the complex structures as coupled multipole modes with highest enhancements obtained due to superposition of high-order modes in small particles. The model allows one to optimize the structures for the largest possible field enhancements, which depends on the quality factor Q of the metal and can be as high as Q2 for two spherical particles. The hot spot can occur either in the nanogaps between the particles or near the smaller particles. We trace the optimum field enhancement mechanism to the fact that the extended dipole modes of larger particles act as efficient antennas, while the modes in the gaps or near the smaller particles act as the compact subwavelength cavities. The present analytical approach can be conveniently extended to incorporate large numbers of particles in various intricate arrangements. [ABSTRACT FROM AUTHOR]

We develop an analytical model of the phase-locking mechanism for diffraction-coupled arrays of semiconductor lasers. While the phase-locking range is found to be limited by nonuniformities between the individual lasers, increasing the gain-index coupling can expand this range. Detailed computer simulations confirm these predictions. Recommendations are made for using arrays of surface-emitting lasers to improve the stability of phase locking. [ABSTRACT FROM AUTHOR]

We show that strong optically induced intervalence band transitions in type-Il InAs/GaSb/AISb quantum wells lead to reverse saturable absorption, and propose to apply it to optical limiting in the mid-infrared spectral region. A salient feature of the proposed limiter is the flexibility of the design for different wave- lengths and threshold powers. We develop a rigorous theoretical model of the proposed limiter, and use it to estimate the relation- ship between the key figures of merit: insertion loss, threshold, optical bandwidth and dynamic range. We investigate tradeoffs involving the dynamic range, optical bandwidth and thickness of the limiter, and show that one can attain a favorable combination of these. [ABSTRACT FROM AUTHOR]

In this paper, we identify the main reason impeding coherent generation of phonons in solid state — the inherently high density of phonon states. Based on the results of our analysis we formulate a set of conditions that may make phonon lasing practical and point out the most promising mechanism of phonon lasing: LO → LA + TO in InP. We then develop a complete set of phonon laser equations and evaluate the threshold, output power and efficiency of phonon lasers based on InP MESFET. We show that one can obtain high-power 1.26-THz coherent phonon emission with pump power as small as a few milliwatts and up to 5% slope efficiency. Potential applications are also discussed. [ABSTRACT FROM AUTHOR]

Study the development of a rigorous density-matrix-based theory of lasing based on optically induced or autoionization-induced coherence between the levels. Establishment of the connection between the lasing without inversion and Raman and parametric processes; Implications of lasings on intersubband lasers.

Considers backward optical parametric oscillators and amplifiers. Pump intensity; Second-order nonlinear optical domains; Signal determination; Dependencies of the gain on the normalized pump.

We consider the issue of compensating the loss in plasmonic waveguides with semiconductor gain material and show that, independent of specific geometry, full loss compensation in plasmonic waveguides with significantly sub-wavelength light confinement (less than λ/4n) requires current density well in excess of 100 kA/cm2. This high current density is attributed to the unavoidable shortening of recombination time caused by the Purcell effect inherent to sub-wavelength confinement. Consequently, an injection-pumped plasmonic laser that is truly sub-wavelength in all three dimensions ('spaser') would have threshold current densities that are hard to obtain in any conceivable semiconductor device. [ABSTRACT FROM AUTHOR]

We show that, for the resonant metal-dielectric structures with sub-wavelength confinement of light in all three dimensions, the loss cannot be reduced considerably below the loss of the metal itself unless one operates in the far IR and THz regions of the spectrum or below. Such high losses cannot be compensated by introducing gain due to Purcell-induced shortening of recombination times. The only way low loss optical meta-materials can be engineered is with, as yet unknown, low loss materials with negative permittivity. [ABSTRACT FROM AUTHOR]

We develop a physically transparent model to interpret the sub-wavelength imaging with metal slabs. The model is applied to analyze the optical transfer function (OTF) and show how OTF is affected by the geometric and material parameters. [ABSTRACT FROM AUTHOR]

A density-matrix based theory of transport and lasing in quantum-cascade lasers reveals that large disparity between luminescent linewidth and broadening of the tunneling transition changes the design guidelines to favor strong coupling between injector and upper laser level. This conclusion is supported by the experimental evidence. [ABSTRACT FROM AUTHOR]

The impact of the interface roughness on intersubband transitions (ISTs) in quantum wells is analyzed as an inhomogeneous broadening due to localization rather than a traditional scattering process. The results offer simple explanation for the temperature dependent spectra of gain and absorption in quantum cascade lasers and also for the strong IST polariton phenomena. [ABSTRACT FROM AUTHOR]

We analyze the influence of isotope disorder on longitudinal optical (LO) phonon modes in GaN and then study the scattering by disordered LO phonons in the channel of high power transistor. Results indicate that as a larger number of LO phonons gets excited, a more efficient cooling of electrons can be accomplished and most of the spurious hot phonon effects can be mitigated leading to significant improvement in the saturation velocity. To the best of our knowledge this is the first ever example of disorder playing constructive role in the performance of room-temperature electronic devices. [ABSTRACT FROM AUTHOR]

The authors develop a rigorous theory of the enhancement of spontaneous emission from a light emitting device via coupling the radiant energy in and out of surface plasmon polaritons (SPPs) on the metal-dielectric interface. Using the GaN/Ag system as an example, the authors show that using SPP pays off only for emitters that have a low luminescence efficiency. [ABSTRACT FROM AUTHOR]

The authors consider propagation of a plasmon polariton on the interface between a metal and a magneto-optical material and show that in presence of transverse magnetic field a strong nonreciprocal phase shift results. This phenomenon can be used to achieve optical isolation action in short nanoplasmonic guides with low insertion loss. [ABSTRACT FROM AUTHOR]

It is shown that intersubband transitions caused by the normal incidence circularly polarized light can cause high degree of spin polarization in modulation doped semiconductor quantum wells, especially narrow band gap ones. The efficiency of the proposed spin-polarizing scheme in the presence of various spin-relaxation mechanisms is evaluated and found to approach 98% under moderate amounts of illumination. Potential applications are discussed. [ABSTRACT FROM AUTHOR]

Using quantum-mechanical analysis, a strain-balanced stack of coupled GaN/AlGaN quantum wells has been engineered for bandwidth-optimized all-optical switching at low switching powers. Intersubband transitions between three conduction subbands provide the basis for the large, fast, nonlinear optical response. Optimized performance for a given symbol rate is obtained by engineering the response time and nonlinear phase shift. [ABSTRACT FROM AUTHOR]

Coupling between the transverse electromagnetic mode of the coplanar strips and transverse acoustic phonon mode in the multilayer piezoelectric structures is considered. It is shown that it leads to the formation of a coupled entity—acoustic cavity polariton, whose frequency and velocity can be adjusted within a very broad range by the proper design of the piezoelectric cavity. The acoustic cavity polaritons can be used in filters, delay lines, and solid-state traveling wave devices for frequencies of up to 100 GHz. [ABSTRACT FROM AUTHOR]

We explore the feasibility of reducing the lifetime of longitudinal optical phonons in InP by injecting coherent longitudinal acoustic modes of frequency given by the difference between those of the longitudinal and transverse optical phonons. Calculations show that a ten-fold reduction in the lifetime can be attained using a 40 mW acoustic source. The increase in the phonon decay should reduce the scattering rate of hot electrons in fast devices. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We propose a semiconductor laser (λapprox. 1.25 μm) whose active region is a type-II multiple-quantum-well structure (AlGaInAs/AlGaAsSb/AlInAs on InP) to lengthen the free-carrier lifetime. Simulations project an order-of-magnitude enhancement of the Q-switched energy per pulse without increasing the pump current. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Demonstrates target displacement measurement and surface profiling using coherence frequency domain reflectometry and the photo-emf optical difference frequency sensor capable of generating steady state dc photocurrents. Simplicity and spatial adaptivity of photo-emf optical frequency sensors.

Studies the heterodyning far-infrared radiation using coherently controlled directional photocurrent in semiconductors. Coherent interaction of one- and two-photon absorption; Evaluation of the sensitivity and detectivity of the method.

Exchange interactions between the holes confined in arrays of strained quantum dots subject to compressive and tensile strain are shown to lead to ferrimagnetic arrangement of magnetic moments. Using example of strained In[sub 1-x]Ga[sub x]As quantum dots on InP substrate, it is shown how magnetic properties of a semiconductor material can be engineered without resorting to doping with magnetic ions, and the Curie temperature is estimated to be of the order of 25 K. Potential applications in information storage and processing are considered. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Measures autocorrelation function of mode-locked laser pulses based on synchronous drift of photogenerated carriers. Interference of a pulse with time-delayed replica in a conventional photoconductor; Generation of a pulsating grating represented as a superposition of moving gratings; Utilization of method in measuring weak pulses.

Examines the direct current in semiconductors. Correlation between second order susceptibility and direct current; Calculation of current densities for bipolar and unipolar devices; Estimation of second harmonic power produced by nonlinear interaction.

Investigates the electric field dependence of the exciton absorption in type II superlattices. Utilization of type II structures in visible spatial light modulators and switches; Presence of the large effective blue shift of the absorption edge; Modulation of the absorption.

Examines the electric field dependence of the optical absorption in the type II superlattices. Need for the efficient electro-optic devices in the visible spectral range; Effects of the small longitudinal electric field on the absorption properties of the superlattices; Details on the broadening of the absorption edge.

Asymmetric molecular bonds possess a microscopic second-order nonlinear optical polarizability p(2). Crystals built from them possess a macroscopic second-order nonlinear optical susceptibility, χ(2), if their structure lacks centrosymmetry. χ(2) can be enhanced by introducing additional asymmetry at the meta-structural level. Here, we use a dipole matrix formalism to calculate χ(2) of asymmetric GaAs/AlGaAs coupled quantum well structures at telecommunication frequencies, for which interband (rather than previously considered intersubband) optical transitions govern optical nonlinearities. Using unit cell and envelope wavefunctions and considering all possible transitions between two bound electron and two bound hole states, we predict tenfold enhancement in χ(2) in previously underexplored ranges of quantum well asymmetry and coupling barrier thickness. This work paves the way toward enhanced, tailorable second-order optical nonlinearities for semiconductor digital alloy and superlattice structures. [ABSTRACT FROM AUTHOR]

A new on‐chip diagnostic tool is developed, allowing for real‐time full characterization of waveguided ultrashort optical pulses. This technique, called transverse frequency‐resolved optical gating (T‐FROG), relies on second harmonic generation (SHG) in a transverse (surface emitting) geometry. The T‐FROG is implemented on a thin‐film lithium niobate (LN) platform, demonstrating its versatility and consistency in accurately characterizing waveguided femtosecond pulses, including information about chirp and self‐phase modulation. In contrast to traditional FROG techniques, T‐FROG represents a significant improvement as it provides temporal amplitude and phase profiles of ultrafast optical pulses directly inside photonic integrated circuits. The real‐time in situ characteristics and dynamics of optical pulses offered by T‐FROG show promise for their potential applications in the design, testing, and optimization of ultrafast photonic integrated circuits. [ABSTRACT FROM AUTHOR]