Multilayer Dielectric Mirrors Research Articles

InAs/InP quantum dot microcavities employing dielectric Bragg mirrors

We investigate the optical emission characteristics of InAs/InP quantum dot microcavities emitting around λ=1.5 μm . Planar and etched-pillar-type microcavities employing multi-layer dielectric Bragg mirrors are demonstrated. For planar cavities we observe a large increase in the cavity mode emission as a function of increasing temperature above 4 K , which is interpreted in terms of carrier trapping within the wetting layer. Pillar-type microcavities show the discrete mode structure expected for full three-dimensional optical confinement.

Multilayer resonances sharpened by grating waveguide resonance

A multilayer planar structure comprising a highly reflective multilayer dielectric mirror and a corrugated waveguide is proposed for use as a narrow passband optical filter. The proposed filter has a much narrower linewidth than a usual Fabry–Perot cavity with two multilayer dielectric mirrors. It is shown that the narrowing of the linewidth is due to the strong spectral dependence of the phase of the wave reflected from the waveguide grating mirror. The shape of the pass band can be made symmetrical by a proper choice of the grating groove profile.

Far-infrared multilayer mirrors

We present a concept for highly reflecting broadband mirrors in the far-infrared. We report on the fabrication of dielectric multilayer mirrors consisting of 1–6 layers of silicon wafers with vacuum gaps in between. By comparison to gold mirrors, we can demonstrate the high reflectivity (>99%) over the frequency range between 40 and 130 cm−1. The measurements are in very good agreement with theoretical predictions.

Smart dust: self-assembling, self-orienting photonic crystals of porous Si.

Micrometer-sized one-dimensional photonic crystals of porous Si that spontaneously assemble, orient, and sense their local environment are prepared. The photonic crystals are generated by electrochemically etching two discrete porous multilayered dielectric mirrors into Si, one on top of the other. The first mirror is chemically modified by hydrosilylation with dodecene before the etching of the second mirror, which is prepared with an optical reflectivity spectrum that is distinct from the first. The entire film is removed from the substrate, and the second mirror is then selectively modified by mild thermal oxidation. The films are subsequently fractured into small particles by sonication. The chemically asymmetric particles spontaneously align at an organic liquid-water interface, with the hydrophobic side oriented toward the organic phase and the hydrophilic side toward the water. Sensing is accomplished when liquid at the interface infuses into the porous mirrors, inducing predictable shifts in the optical spectra of both mirrors.

Photonic bandgap materials and structures by sol–gel processing

The sol–gel method is an inexpensive and flexible liquid phase processing technique that is suitable for the fabrication of 1-D photonic bandgap structures, such as multilayer dielectric mirrors. In the present work, we started by preparing highly reflecting quarter-wave multilayer stacks, composed of alternating films of high refractive index material (TiO2) and low refractive index material (SiO2), possessing well-defined stop bands. For example, for a 11-layer stack, a stop band was obtained with more than 96% reflectance (at near-normal incidence) between ∼600 and 700 nm, with a gap to mid-gap ratio Δλ/λmax=15.4%. Fabry–Perot micro-cavities, containing high or low index defects within the quarter-wave stack, were also prepared and tested. Such structures were optimized with the help of suitable modeling, using transfer matrix techniques. Various experimental techniques were used to characterize these multilayers, including ellipsometry, visible spectroscopy, X-ray diffraction and atomic force microscopy.

Layer Thickness Error Dependence of the Laser-Induced Damage Threshold of Multilayer Mirrors for High-Power Lasers

We clarified experimentally that layer thickness error significantly affects the laser-induced damage threshold (LIDT) of multilayer laser mirrors. The layer thickness error causes a shift of the maximum-reflectance wavelength (λc) of the mirror from the design wavelength (=laser wavelength λ0). The shift Δλ (=λc-λ0) dependence of the LIDTs of the dielectric multilayer mirrors for 1053, 527, and 355 nm lasers was measured. The LIDT decreased as the |Δλ| increased and was laser-wavelength dependent.

Covalent crosslinking of 1-D photonic crystals of microporous Si by hydrosilylation and ring-opening metathesis polymerization.

Free-standing porous Si multilayer dielectric mirrors, prepared by electrochemical etching of crystalline Si, are treated with a ruthenium ring-opening metathesis polymerization (ROMP) catalyst followed by norbornene to produce flexible, stable composite materials in which poly(norbornene) is covalently attached to the porous Si matrix.

Modeling and Fabrication of Hollow Optical Waveguide for Photonic Integrated Circuits

We present the design and fabrication of hollow optical waveguides with highly reflective mirrors on the guiding walls of waveguides. We demonstrate the possibility of polarization-insensitive and low-loss slab waveguides by loading properly designed dielectric multilayer mirrors. We also propose a novel three-dimensional (3D) hollow waveguide with an etched groove structure for confining light in a lateral direction. We also predict that the propagation constant is independent of the ambient temperature, resulting in temperature-insensitive photonic waveguide devices such as optical filters and grating optical demultiplexers. We fabricate slab and 3D hollow optical waveguides with Au coating and present their propagation characteristics. The propagation loss of a slab waveguide was 1–2 dB/cm and 3–4 dB/cm for transverse electric (TE) and transverse magnetic (TM) modes, respectively. We also suggest the possibility of low-loss 3D hollow waveguides.

A narrow-band optical filter based on a corrugated one-dimensional photonic crystal

A narrow-band optical filter based on a multilayer dielectric mirror deposited onto a corrugated substrate is proposed and investigated. It is shown that, by optimising the thickness of the mirror layers and depth of corrugations, it is possible to obtain a filter with a pass band two orders of magnitude narrower than that of a standard flat filter with a half-wavelength layer surrounded by multilayer dielectric mirrors with the same number of layers as in the filter proposed. It is also shown that the range of angular tuning of the wavelength at which the maximum transmission is achieved is determined by the requirements to the value of losses in this filter. In particular, at permissible losses of 0.8 %, the wavelength tuning range reaches 20 nm for a filter transmission pass band of 0.08 nm.

Subwavelength patterns and high detection efficiency in fluorescence correlation spectroscopy using photonic structures

We present theoretical and experimental evidence of subwavelength resolution and high detection efficiency in fluorescence correlation spectroscopy (FCS) using photonic structures. We show that multilayered dielectric mirrors or metallic mirrors may be used in a conventional FCS setup to improve fluorescence detection and fluctuation analysis.

Simultaneous measurement of the fundamental and third harmonic FEL at LEBRA

Lasing of a free electron laser (FEL) at a wavelength of 1.5 µm has been achieved at Laboratory for Electron Beam Research and Application (LEBRA), Nihon University. In order to study its characteristics in detail, a measurement system for the fundamental and the 3rd harmonic radiation was set up. In this system the visible and the infrared light beams are separated from each other using a commercial cold mirror which is a kind of dielectric multi-layer mirrors. The system made it possible to obtain several FEL parameters simultaneously, such as the yield, the beam profile and the spectrum. It will be useful for the investigation into a phenomena that seems to be the non-linear higher harmonics discussed in recent study on the self amplified spontaneous emission.

Low-loss asymptotically single-mode propagation in large-core OmniGuide fibers

We present the light-propagation characteristics of OmniGuide fibers, which guide light by concentric multi-layer dielectric mirrors having the property of omnidirectional reflection. We show how the lowest-loss TE_01 mode can propagate in a single-mode fashion through even large-core fibers, with other modes eliminated asymptotically by their higher losses and poor coupling, analogous to hollow metallic microwave waveguides. Dispersion, radiation leakage, material absorption, nonlinearities, bending, acircularity, and interface roughness are considered with the help of leaky modes and perturbation theory, and both numerical results and general scaling relations are presented. We show that cladding properties such as absorption and nonlinearity are suppressed by many orders of magnitude due to the strong confinement in a hollow core, and other imperfections are tolerable, promising that the properties of silica fibers may be surpassed even when nominally poor materials are employed.

Broad-band dielectric multilayer mirrors by period staggering

A simple interferometric method is deduced for staggering assemblies of periods formed of double layers, a high- and a low-index film, to highly reflect a broad region of the spectrum. The dispersion of the materials used are included in the design procedure. Unlike layer-staggering methods, the method presented here performs staggering for the periods, forming the assembly, and not the individual layers. The periods forming these staggered systems are defined as achromatic periods. Designs employing this method are presented and the results are discussed.

Simple method for optimisation of parameters of a combined diffraction grating at grazing incidence

A method for optimising parameters of combined structures consisting of a dielectric diffraction grating and a metal or a multilayer dielectric mirror is proposed. The method is based on the use of waveguide properties of a combined diffraction grating. Its main advantage is that one can determine the optimum parameters of a combined grating without solving the diffraction problem.

Autocollimation diffraction gratings based on waveguides with leakage modes

It is shown that the leakage modes of multilayer corrugated dielectric and metal-dielectric structures are extremely important for the achievement of high efficiency of such structures as diffraction gratings. Three types of grating structures are considered: a corrugated waveguide layer on a flat multilayer dielectric mirror (type 1); a multilayer dielectric mirror on a corrugated substrate (i.e., a totally corrugated structure) (type 2); and a structure of the intermediate type (type 3). The performance characteristics of these structures used in the Littrow mounting are compared.

Omnidirectional reflection by multilayer dielectric mirrors

Periodic structures reflect strongly at frequencies and angles of incidence corresponding to photonic bandgaps. It has recently been shown that for a suitable choice of high and low refractive indices nh and nl, a high-low dielectric multilayer can reflect strongly at all angles of incidence. An accurate and simple analytic approximation for the location of the band edges for the s and p polarizations is given. The region in the (nl,nh) plane where omnidirectional reflection occurs is determined. This region lies above a curve which has its minimum value of nh(≈2.247n1) at nl≈1.492n1, where n1 is the refractive index of the medium of incidence. The minimum occurs when the optical paths in the high and low refractive index layers are in the ratio 1.362 to 1.

Combined Diffraction Grating in the Scheme of Grazing Incidence: Calculation and Parameter Optimization

The method of parameter optimization of combined structures, which consist of a dielectric grating and a metallic or multilayer dielectric mirror, was proposed. It is based on the use of the waveguide properties of the combined diffraction grating. Its main advantage lies in the possibility of determining the optimum parameters of the combined grating without solving the diffraction problem.

Near ultraviolet optically pumped vertical cavity laser

Optically pumped near ultraviolet vertical cavity laser operation (VCSEL) has been obtained under quasi-continuous wave conditions at room temperature near 383 nm from shallow InGaN/GaN multiple quantum wells (MQWs). Low loss optical resonators were fabricated by using in-situ grown (Al,Ga)N distributed Bragg reflectors that featured strain engineering design for high optical morphology, in combination with low-loss dielectric multilayer mirrors.

Ultrashort Pulse Generation by Mode-Locked Solid-State Lasers.

Recent progress on mode-locked solid-state lasers in the femtosecond region is reviewed. Dispersiondesigned dielectric multilayer mirror is an ideal device to compensate the intra-cavity group-delay dispersion of the femtosecond mode-locked lasers. Semiconductor saturable absorber mirrors improve reliability of the mode-locked lasers without any pulse-broadening. With these two types of functional mirrors, stable sub-5fs optical pulse is generated directly from a Ti: sapphire laser oscillator.

Multilayer “dielectric” mirror for atoms

All existing atomic mirrors are conceptually similar to metallic mirrors in standard optics in the sense that they are constructed with repulsive potentials and thus produce an imaginary ``refraction index.'' Here a different kind of mirror for atoms that is similar to a multilayer dielectric mirror in standard optics is proposed. We show that a periodic attractive laser potential can reflect atoms of certain momenta due to the presence of gaps in the spectrum of energies, as in the photonic band-gap structures in light optics. Spontaneous emission and gravitational effects are also analyzed.