Thermo-optic VO2-based silicon waveguide mid-infrared router with asymmetric activation thresholds and large bi-stability.

We report a novel four-port optical router that exploits non-linear properties of vanadium dioxide (VO2) phase-change material to achieve asymmetrical power threshold response with power limiting capability. The scope of this study lies within the concept, modeling, and simulation of the device, with practical considerations in mind for future experimental devices. The waveguide structure, designed to operate at the wavelength of 5.0 µm, is composed of a silicon core with air and silicon dioxide forming the cladding layers. Two ring resonators are employed to couple two straight waveguides, thus four individual ports. One of the ring resonators has a 100-nm-thick VO2 layer responsible for non-linear behavior of the device. The router achieves 56.5 and 64.5 dB of power limiting at the forward and reverse operating modes, respectively. Total transmission in the inactivated mode is 75%. Bi-stability and latching behavior are demonstrated and discussed.

Thermo-optic VO2-based silicon waveguide mid-infrared router with asymmetric activation thresholds and large bi-stability: errata.

The authors report an error in the phrasing and citation of the reference to simulation model input data in [Opt. Express31(14), 23260202310.1364/OE.493895]. The original phrasing misplaced "heat capacity" after the in-text citation, where the intended phrase was "electrical conductivity," and heat capacity was intended to be cited with thermal conductivity as external measured data. In the reference itself, the source cited for thermal conductivity and heat capacity was errantly cited as H. Kizuka, et al., Jpn. J. Appl. Phys.54, 053201 (2015)10.7567/JJAP.54.053201. The JJAP paper shows data for both thermal properties of VO2; however, the data utilized for our model input parameters are found in [J. Miranda, et al., Phys. Rev. B 98, 075144 (2018)], including heat capacity data reproduced therein from [T. Kawakubo and T. Nakagawa, J. Phys. Soc. Jap. 19, 4 (1964)]. There are no effects on the simulated data nor conclusions of this article due to the error.

A reflective millimeter-wave photonic limiter.

Millimeter-wave (mm-wave) communications and radar receivers must be protected from high-power signals, which can damage their sensitive components. Many of these systems arguably can be protected by using photonic limiting techniques, in addition to electronic limiting circuits in receiver front-ends. Here we demonstrate, experimentally and numerically, a free-space, reflective mm-wave limiter based on a multilayer structure involving a nanolayer of vanadium dioxide VO2, which experiences a heat-related insulator-to-metal phase transition. The multilayer acts as a variable reflector, controlled by the incident wave intensity. At low intensities VO2 remains dielectric, and the multilayer exhibits strong resonant transmittance. When the incident intensity exceeds a threshold level, the emerging metallic phase renders the multilayer highly reflective while safely dissipating a small portion of the input power, without damage to the limiter. In the case of a Gaussian beam, the limiter has a nearly constant output above the limiting threshold input.

Resonant cavities with phase-changing materials.

Phase changing materials are commonly used for optical switching, limiting, and sensing. In many important cases, the change in the transmission characteristics of the optical material is caused by light-induced heating. We demonstrate that the incorporation of such optical materials in judiciously designed photonic structures can dramatically alter the light-induced phase change, as well as the transmission characteristics of the entire photonic structure. Possible practical implications are discussed.

Hypersensitive Transport in Photonic Crystals with Accidental Spatial Degeneracies.

A localized mode in a photonic layered structure can develop nodal points (nodal planes), where the oscillating electric field is negligible. Placing a thin metallic layer at such a nodal point results in the phenomenon of induced transmission. Here we demonstrate that if the nodal point is not a point of symmetry, then even a tiny alteration of the permittivity in the vicinity of the metallic layer drastically suppresses the localized mode along with the resonant transmission. This renders the layered structure highly reflective within a broad frequency range. Applications of this hypersensitive transport for optical and microwave limiting and switching are discussed.

Degenerate band edge resonances in coupled periodic silicon optical waveguides.

Using full three-dimensional analysis we show that coupled periodic optical waveguides can exhibit a giant slow light resonance associated with a degenerate photonic band edge. We consider the silicon-on-insulator material system for implementation in silicon photonics at optical telecommunications wavelengths. The coupling of the resonance mode with the input light can be controlled continuously by varying the input power ratio and the phase difference between the two input arms. Near unity transmission efficiency through the degenerate band edge structure can be achieved, enabling exploitation of the advantages of the giant slow wave resonance.

Taming the flow of light via active magneto-optical impurities.

We demonstrate that the interplay of a magneto-optical layer sandwiched between two judiciously balanced gain and loss layers which are both birefringent with misaligned in-plane anisotropy, induces unidirectional electromagnetic modes. Embedding one such optically active non-reciprocal unit between a pair of birefringent Bragg reflectors, results in an exceptionally strong asymmetry in light transmission. Remarkably, such asymmetry persists regardless of the incident light polarization. This photonic architecture may be used as the building block for chip-scale non-reciprocal devices such as optical isolators and circulators.

Frozen light in photonic crystals with degenerate band edge.

Consider a plane monochromatic wave incident on a semi-infinite periodic structure. What happens if the normal component of the transmitted wave group velocity vanishes? At first sight, zero normal component of the transmitted wave group velocity simply implies total reflection of the incident wave. But we demonstrate that total reflection is not the only possible outcome. Instead, the transmitted wave can appear in the form of a frozen mode with very large diverging amplitude and either zero, or purely tangential energy flux. The field amplitude in the transmitted wave can exceed that of the incident wave by several orders of magnitude. There are two qualitatively different kinds of frozen mode regime. The first one is associated with a stationary inflection point of electromagnetic dispersion relation. This phenomenon has been analyzed in our previous papers. Now, our focus is on the frozen mode regime related to a degenerate photonic band edge. An advantage of this phenomenon is that it can occur in much simpler periodic structures. This spectacular effect is extremely sensitive to the frequency and direction of propagation of the incident plane wave. These features can be very attractive in a variety of practical applications, such as higher harmonic generation and wave mixing, light amplification and lasing, highly efficient superprizms, etc.

Gigantic transmission band-edge resonance in periodic stacks of anisotropic layers.

We consider Fabry-Perot cavity resonance in periodic stacks of anisotropic layers with misaligned in-plane anisotropy at the frequency close to a photonic band edge. We show that in-plane dielectric anisotropy can result in a dramatic increase in field intensity and group delay associated with the transmission resonance. The field enhancement turns out to be proportional to fourth degree of the number N of layers in the stack. By contrast, in common periodic stacks of isotropic layers, those effects are much weaker and proportional to N2 Thus, the anisotropy allows one to drastically reduce the size of the resonance cavity with similar performance. The key characteristic of the periodic arrays with gigantic transmission resonance is that the dispersion curve omega(k) at the photonic band edge has the degenerate form Deltaomega approximately (Deltak)4, rather than the regular form Deltaomega approximatley (Deltak)2. This can be realized in specially arranged stacks of misaligned anisotropic layers. The degenerate band-edge cavity resonance with similar outstanding properties can also be realized in a waveguide environment, as well as in a linear array of coupled multimode resonators, provided that certain symmetry conditions are in place.