Asymmetric Fabry-Perot Resonator Research Articles

A coating design to rule them all: asymmetric Fabry-Perot resonators with diverse optical response based on Au films with high-temperature sensitivity.

Thermal annealing of thin metal films induces morphology changes that have a dramatic effect in the optical properties. Here we propose an asymmetric Fabry-Perot resonator consisting of a top metal film, a dielectric spacer, and a bottom metal mirror that can display a diverse infrared response. Thermally induced morphology changes result in large reflectivity variations within a limited temperature range following the top film transition between conductive, highly lossy, and transparent regimes. This behavior arises from the combination of the top film properties with interference effects in the multilayer. Furthermore, the proposed structure holds promise for potential sensing applications, as its optical response displays four times larger temperature sensitivity than a single film.

Peculiarities of reflection and transmission matrices of a system with magneto-optical activity and asymmetric transmission

We consider and compare the peculiarities of nonreciprocal optical properties of the following three systems: a) a planar layer of cholesteric liquid crystal (CLC) in the external magnetic field directed along the CLC helix axis, b) an asymmetric Fabry-Perot resonator with a planar CLC layer inside and, finally, c) an asymmetric Fabry-Perot resonator with a planar CLC layer inside in an external magnetic field, again, directed along CLC’s axis. We investigate the specific properties of matrices of reflection and transmission of such systems in all their details. Then we study the influence of absorption on nonreciprocal optical properties of these systems. Nonreciprocity depends on the polarization of the incident light in the absence/presence of absorption in such systems; while nonreciprocity appears for naturally polarized incident light in these systems only in the presence of absorption in the system. Nonreciprocity appears for naturally polarized incident light also in photonic crystals with the helix period gradient.

Thin film-based Gires–Tournois Resonator (GTR) as quasi-optical analogue of the Thomas rotation angle effect in special relativity

We present an unconventional approach to generate an optical analogue of the Thomas rotation angle found in Special Relativity (SR) by using a thin-film–based Gires–TournoisResonator (GTR). At first glance, the phase response of the GTR seems to fail as an optical analogue for the Thomas rotation angle in the phase domain but we demonstrate that an analogue can be successfully constructed in the intensity domain by combining the GTR with a Michelson interferometer (MI), thus forming an interferometer known as the Michelson–Gires–Tournois Interferometer (MGTI). Thomas rotation angle is a spatial rotation of the reference frame due to the Einstein velocity addition (EVA) law of two successive relativistic velocities travelling in non-collinear directions, whereas, the GTR is a thin-film based asymmetric Fabry–Perot resonator (FPR) with a partially reflecting front mirror, and a 100% rear-reflecting mirror. We investigate in detail, both analytically and numerically, the Thomas rotation angle’s full behaviour under various parameter conditions. This approach offers the following advantages: (i) it leads to a simpler overall configuration, (ii) it measures the Thomas rotation angle directly requiring only a single optical parameter instead of multiple parameters compared with other methods, and (iii) it requires no sophisticated multilayer thin film design.

High-Speed, Phase-Dominant Spatial Light Modulation with Silicon-Based Active Resonant Antennas

Spatiotemporal control of optical wavefronts is of great importance in numerous free-space optical applications including imaging in 3D and through scattering media, remote sensing, and generation of various beam profiles for microscopy. Progress in these applications is currently limited due to lack of compact and high-speed spatial light modulators. Here we report an active antenna comprising a free-space coupled asymmetric Fabry–Perot resonator that produces a phase-dominant thermo-optic modulation of reflected light at frequencies approaching tens of kilohertz. As a proof of concept for spatial light modulation, we demonstrate a 6 × 6 array of such active antennas with beam deflection capability. The robust design of our silicon-based active antenna will enable large-scale integration of high-speed, phase-dominant spatial light modulators.

Tunable metasurfaces via subwavelength phase shifters with uniform amplitude

Metasurfaces with tunable spatial phase functions could benefit numerous applications. Currently, most approaches to tuning rely on mechanical stretching which cannot control phase locally, or by modulating the refractive index to exploit rapid phase changes with the drawback of also modulating amplitude. Here, we propose a method to realize phase modulation at subwavelength length scales while maintaining unity amplitude. Our device is inspired by an asymmetric Fabry-Perot resonator, with pixels comprising a scattering nanopost on top of a distributed Bragg reflector, capable of providing a nearly 2π nonlinear phase shift with less than 2% refractive index modulation. Using the designed pixels, we simulate a tunable metasurface composed of an array of moderately coupled nanopost resonators, realizing axicons, vortex beam generators, and aspherical lenses with both variable focal length and in-plane scanning capability, achieving nearly diffraction-limited performance. The experimental feasibility of the proposed method is also discussed.

Direct Measurement of Thermal Emission From a Fabry–Perot Cavity Resonator

There have been growing interests in selective control of thermal emission by using micro/nanostructures. The present study describes direct measurements of infrared thermal emission at elevated temperatures of an asymmetric Fabry–Perot resonator at variable angles for each polarization. The multilayered structure mainly contains a SiO2 optical cavity sandwiched between a thick (opaque) Au film and a thin Au film. Metallic adhesive and diffusion-barrier layers were deposited on a Si substrate before depositing the thick Au film. A dielectric protection layer was deposited atop the thin Au film to prevent oxidation at high temperatures. A SiC wafer was used as the reference to test the emittance measurement facility, which includes a heated sample holder, a blackbody source, mirror assembly, a polarizer, and a Fourier-transform infrared spectrometer with different detectors. The measured emittance spectra of the Fabry–Perot structure exhibit peak broadening and shifting as temperature increases; the mechanisms are elucidated by comparison with theoretical modeling.

C-band side-entry Ge quantum-well electroabsorption modulator on SOI operating at 1 V swing

An electroabsorption modulator using a side-entry architecture achieved a contrast ratio exceeding 3 dB over a 3.5 nm range in the C-band, using a voltage swing of 1 V and operating at 100°C. Modulation was due to the quantum-confined Stark effect from ten Ge/SiGe quantum wells epitaxially grown on silicon-on-insulator (SOI) wafers. The device exploits an asymmetric Fabry-Perot resonator formed between the totally internally reflecting air-SiGe interface and a frustrated total internal reflection from the buried oxide layer of the SOI substrate.

Optical modulator on silicon employing germanium quantum wells

We demonstrate an electroabsorption modulator on a silicon substrate based on the quantum confined Stark effect in strained germanium quantum wells with silicon-germanium barriers. The peak contrast ratio is 7.3 dB at 1457 nm for a 10 V swing, and exceeds 3 dB from 1441 nm to 1461 nm. The novel side-entry structure employs an asymmetric Fabry-Perot resonator at oblique incidence. Unlike waveguide modulators, the design is insensitive to positional misalignment, maintaining > 3 dB contrast while translating the incident beam 87 mum and 460 mum in orthogonal directions. Since the optical ports are on the substrate edges, the wafer top and bottom are left free for electrical interconnections and thermal management.

Asymmetric Fabry-Perot resonator containing an arbitrary inhomogeneous layer

A new method for determining the transmission and reflection coefficients for an arbitrarily polarized electromagnetic wave incident obliquely on an inhomogeneous insulating layer inside an asymmetric Fabry-Perot resonator is proposed. Algebraic relationships between these coefficients for a layer bounded by different homogeneous semi-infinite media and for the same layer in a vacuum are derived. Three examples corresponding to real situations are analyzed, and the results of corresponding numerical calculations are discussed.

Bragg thickness criterion for intracavity diffraction gratings

The grating thickness limit lFP between the Raman–Nath and the Bragg diffraction regimes is calculated for an index grating placed in an asymmetric Fabry–Perot resonator with a totally reflecting back mirror and compared with that which was obtained for the same grating with no cavity lM. Owing to the increase of the effective interaction length inside the Fabry–Perot cavity, the stronger the front mirror reflectivity R1 of the cavity, the smaller the thickness above which the whole diffracted intensity can be concentrated into one unique diffracted beam: lFP=[(1-R1)/(1+R1)]lM/2.

Fabry–Perot-enhanced self-electro-optic-effect devices

Optically bistable symmetric self-electro-optic-effect devices that use an asymmetric Fabry-Perot resonator are demonstrated and assessed. Contrast ratios exceeding 30 for low bias levels (under 6 V) are measured for low intensities. The Fabry-Perot self-electro-optic-effect device is also shown to saturate readily with intensity, with the contrast ratio decreasing by a factor of 3 for an irradiance of 10 microW/microm(2). Wavelength sensitivity measurements and calculations are also presented.

Optically addressed asymmetric Fabry–Perot modulator

A low power, high contrast optically addressed modulator, operating with normal incidence, has been fabricated. Optically controlled reflection modulation is achieved through optically induced absorption modulation in a periodically δ-doped InGaAs/GaAs multiple quantum well structure inserted in an integrated asymmetric Fabry–Perot resonator. A contrast ratio≳60:1 was measured using a spectrally matched low power InGaAs/GaAs quantum well laser to generate the write (control) signal. The insertion loss for the normally off modulator is 4.6 dB at the highest write signal power (30 mW) used. The device lends itself to the fabrication of arrays for optically addressed spatial light modulation.

Novel reflectance modulator employing an InGaAs/AlGaAs strained-layer superlattice Fabry–Perot cavity with unstrained InGaAs/InAlAs mirrors

We present a novel approach to optoelectronic devices by combining mechanically stable strained and unstrained epitaxial multilayers. We illustrate our approach with an optical reflectance modulator based on an asymmetric Fabry–Perot resonator designed to operate near 1.06 μm. The resonator is grown on a mechanically relaxed buffer of In0.11Ga0.89As deposited on a GaAs substrate. For mirrors, quarter-wave stacks of In0.11Ga0.89As and In0.1Al0.9As, lattice matched to the buffer, are used. The Fabry–Perot cavity consists of an In0.23Ga0.77As/Al0.35Ga0.65As strained-layer superlattice whose planar lattice constant also matches the buffer. Our first device operates at 1.04–1.05 μm depending on lateral position across the wafer. The insertion loss at resonance is less than 2 db and a fractional modulation of over 60% has been achieved with a 4 V bias swing.