We present a $\mathbf{k} \cdot \mathbf{p}$ theory of photonic crystals containing gain and loss in which the gain and loss are added to separate primitive cells of the underlying Hermitian system, thereby creating a supercell photonic crystal. We show that the supercell bands of this system can merge outward from the degenerate contour formed from folding the bands of the underlying Hermitian system into the supercell Brillouin zone, but that other accidental degeneracies in the band structure of the underlying Hermitian system do not yield band merging behavior. Finally, we show that the modal coupling matrix in PhCs with balanced gain and loss is trace-less, and thus the imaginary components of the eigenvalues can only move relative to one another as the strength of the gain and loss is varied, without any collective motion.
Systems with coupled cavities and waveguides have been demonstrated as optical switches and optical sensors. To optimize the functionalities of these optical devices, Fano resonance with asymmetric and steep spectral line shape has been used. We theoretically propose a coupled photonic crystal cavity-waveguide structure to achieve Fano resonance by placing partially reflecting elements in waveguide. To enhance Fano resonance, optical gain material is introduced into the cavity. As the gain increases, the transmission line shape becomes steepened and the transmissivity can be six times enhanced…
In this paper, by cascading several bichromatic photonic crystals we demonstrate that the quality factor can be much larger compared with that in an isolated cavity without increasing the total size of the device. We take lithium niobate photonic crystal as an example to illustrate that the simulated quality factor of the cascaded cavity can attain 10^5 with a 70° slant angle, which is an order of magnitude larger than that in isolated cavity. The device can be fabricated easily by current etching technique for lithium niobate. We have fabricated the proposed device experimentally including ho…
Integrated ytterbium gain for visible-near-infrared photonics
John A. Paulson School of Engineering and Applied Sciences, Harvard University（哈佛大学生物工程与应用科学学院）；Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology（麻省理工学院电气与计算机科学系）；Electrical, Computer and Energy Engineering, University of Colorado, Boulder（科罗拉多大学博尔德分校电气、计算机和能源工程系）；Chi3 Optics LLC（Chi3光学有限责任公司）；Octave Photonics（Octave光子学公司）；Time and Frequency Division, National Institute of Standards and Technology（美国国家标准与技术研究院时间与频率司）；Department of Physics, University of Colorado Boulder（科罗拉多大学博尔德分校物理系）
The ability to amplify optical signals is of pivotal importance across science and technology. The development of optical amplifiers has revolutionized optical communications, which are today pervasively used in virtually all sensing and communication applications of coherent laser sources. In the telecommunication bands, optical amplifiers typically utilize gain media based on III-V semiconductors or rare-earth-doped fibers. Another way to amplify optical signals is to utilize the Kerr nonlinearity of optical fibers or waveguides via parametric processes. Such parametric amplifiers of travell…
Photonic crystals have provided a controllable platform to examine excitingly new topological states in open systems. In this work, we reveal photonic topological corner states in a photonic graphene with mirror-symmetrically patterned gain and loss. Such a nontrivial Wannier-type higher-order topological phase is achieved through solely tuning on-site gain/loss strengths, which leads to annihilation of the two valley Dirac cones at a time-reversal-symmetric point, as the gain and loss change the effective tunneling between adjacent sites. We find that the symmetry-protected photonic corner mo…
Parity-time (PT) symmetry and broken in micro/nano photonic structures have been investigated extensively as they bring new opportunities to control the flow of light based on non-Hermitian optics. Previous studies have focused on the situations of PT-symmetry broken in loss-loss or gain-loss coupling systems. Here, we theoretically predict the gain-gain and gain-lossless PT-broken from phase diagram, where the boundaries between PT-symmetry and PT-broken can be clearly defined in the full-parameter space including gain, lossless and loss. For specific micro/nano photonic structures, such as c…
We design photonic structures embedding different functional molecular systems of photochromic switching and lasing. We study the light absorption of two photochromic molecules and of 4,4'-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) with density functional theory. For the photochromic diarylethene we derivate the refractive index with Kramers-Kronig relations and we design multilayer photonic structures alternating diarylethene with either poly vinyl carbazole or fluorine indium co-doped cadmium oxide (FICO) nanoparticlebased layers. For BSB-Cz we design a one-dimensional photonic crystal altern…
We measure the dynamics of the thermo-optical nonlinearity of both a mode-gap nanocavity and a delocalized mode in a Ga$_{\mathrm{0.51}}$In$_{\mathrm{0.49}}$P photonic crystal membrane. We model these results in terms of heat transport and thermo-optical response in the material. By step-modulating the optical input power we push the nonlinear resonance to jump between stable branches of its response curve, causing bistable switching. An overshoot of the intensity followed by a relaxation tail is observed upon bistable switching. In this way, the thermal relaxation of both the localized resona…
The effects of gain and loss on the band structures of a bulk topological dielectric photonic crystal (PC) with $C_{6v}$ symmetry and the PC-air-PC interface are studied based on first-principle calculation. To illustrate the importance of parity-time (PT) symmetry, three systems are considered, namely the PT-symmetric, PT-asymmetric, and lossy systems. We find that the system with gain and loss distributed in a PT symmetric manner exhibits a phase transition from a PT exact phase to a PT broken phase as the strength of the gain and loss increases, while for the PT-asymmetric and lossy systems…
We consider particle-hole symmetric photonic graphene with balanced gain and loss. We show that edge states with purely imaginary eigenvalues appear along the zigzag edge. We propose an idea that these edge states are protected by spontaneously broken particle-hole symmetry. We discuss that the edge states are topological in the sense that the exceptional rings are robust against symmetry protecting disorder. If the disorder is too strong to restore the spontaneously broken particle-hole symmetry, then such protection of the edge states is lost.
Giant backward Brillouin interaction in generic InP integrated photonics
Nonlinear Nanophotonics Group, MESA+ Institute of Nanotechnology, University of Twente（特温特大学非线性纳米光子学小组、MESA+纳米技术研究所）；Photonic Integration Group, Department of Electrical Engineering, Eindhoven University of Technology（埃因霍芬理工大学电气工程学院光子集成小组）
Tunable lasers emitting at a 2-3 $μ$m wavelength range and compatible with photonic integration platforms are of great interest for sensing applications. To this end, combining GaSb-based semiconductor gain chips with Si$_3$N$_4$ photonic integrated circuits offers an attractive platform. Herein, we exploit the low-loss features of Si$_3$N$_4$ waveguides and demonstrate a hybrid laser comprising a GaSb gain chip with an integrated tunable Si$_3$N$_4$ Vernier mirror. At room temperature, the laser exhibited a maximum output power of 15 mW and a tuning range of 80 nm (1937-2017 nm). The low-loss…
Dissipative solitons rely on the double balance between nonlinearity and dispersion as well as gain and loss have attracted a lot of attention in optics, since it gives rise to ultrashort pulses and broadband frequency combs with good stability and smooth spectral envelopes. Here we observe a novel dissipative solitons in microwave photonics that gives rise to wideband tunable frequency hopping microwave signals with fast frequency switching speed. The dissipative microwave photonic solitions are achieved through the double balance between nonlinear gain saturation and linear filtering as well…
Topological photonics has emerged as a novel route to engineer the flow of light. Topologically-protected photonic edge modes, which are supported at the perimeters of topologically-nontrivial insulating bulk structures, have been of particular interest as they may enable low-loss optical waveguides immune to structural disorder. Very recently, there is a sharp rise of interest in introducing gain materials into such topological photonic structures, primarily aiming at revolu-tionizing semiconductor lasers with the aid of physical mechanisms existing in topological physics. Examples of re-mark…
In this paper, ultra-broad band optical signal amplification are analyzed and demonstrated by utilizing supercontinuum generation propagating over the photonic crystal fiber. The coupled nonlinear Schroodinger equation containing parametric process and stimulated Raman scattering effect was analyzed and solved to calculate the variation of signal gain with frequency. The dependence of the gain spectra on nonlinear and chromatic dispersion coefficients as well as the geometrical parameters of photonic crystal fiber are discussed. The results show that when using a pump at wavelength 1450nm and …
