Subwavelength Grating Mirror Research Articles

Cryogenic mid-wave infrared hyperspectral Fabry-Perot filter based on a tensile-strained single-layer subwavelength grating mirror.

We report here the first demonstration of a cryogenic mid-wave infrared (MWIR) hyperspectral fixed-cavity Fabry-Perot filter based on a suspended tensile-strained single-layer 2-D subwavelength grating (SWG) mirror. Optical design optimization of the 2-D SWG mirror and parameter tolerance study are performed. For the first time, process control of grating air-hole sidewall angle and the grating air-hole fill-factor fabrication error caused by e-beam lithography electron-scattering effect is reported. At 80 K, namely the operating temperature of MWIR photodetectors, the as-fabricated suspended 2-D SWG mirror has achieved excellent surface flatness with a slight center-to-edge bowing of 15 nm over a 1-mm2 large mirror area and a high average reflectivity of 0.97 across a wavelength range of 3.72-5 µm, which represents an unprecedentedly wide fractional bandwidth Δλ/λc of 30%. The cryogenically cooled Fabry-Perot filter exhibits an unrivaled high spectral resolution of 10 nm that far exceeds the optical requirement for MWIR hyperspectral imaging applications.

What is the best planar cavity for maximizing coherent exciton-photon coupling

We compare alternative planar cavity structures for strong exciton-photon coupling with the conventional distributed Bragg reflector (DBR) and three unconventional types of cavity mirrors—air/GaAs DBR, Tamm-plasmon mirror, and sub-wavelength grating mirror. We design and optimize the planar cavities built with each type of mirror at one side or both sides for the maximum vacuum field strength. We discuss the trade-off between performance and fabrication difficulty for each cavity structure. We show that cavities with sub-wavelength grating mirrors allow simultaneously the strongest field and high cavity quality. The optimization principles and techniques developed in this work will guide the cavity design for research and applications of matter-light coupled semiconductors, especially new material systems that require greater flexibility in the choice of cavity materials and cavity fabrication procedures.

2 μm波段GaSb基亚波长光栅反射镜的设计

2 μm波段GaSb基亚波长光栅反射镜的设计

High reflectivity broadband infrared mirrors with all dielectric subwavelength gratings

A high reflectivity (>99%) subwavelength grating mirror (SWGM), yields a very broad reflection spectrum (1.3–2.1μm), has been designed for parallel polarized (p-polarized) incident light and evaluated by rigorous electromagnetic simulations. Design-sensitive analysis was made by varying one parameter at one time while keeping the other constant. The operating region of the grating mirror can be adjusted by varying the parameters of grating. The results show that the broadband reflection is unaffected by the refractive index and the thickness of the low index material, which is different from the previous conclusions. Because of its ease of fabrication, the mirror can be integrated with any photonic component with a flat surface, which has potential applications for active and passive photonic devices.

Cavity optomechanics with sub-wavelength grating mirrors

We design, fabricate and study a novel platform for cavity optomechanics: a silicon nitride membrane patterned as a sub-wavelength diffraction grating. Using the grating as one mirror of a Fabry–Perot cavity, we realize an optical finesse of F = 2830 ± 60, corresponding to a grating reflectivity of R = 0.998. The finesse we achieve appears to be within a factor of two of the limit set by material absorption. We study the finesse as a function of wavelength and optical spot size in order to elucidate various optical loss mechanisms. We find that the cavity exhibits birefringence, and establish that it, too, is a source of optical loss. We then characterize the mechanical motion. We observe hundreds of normal modes, and find the fluctuating amplitude of one of them to be very well described by a Boltzmann distribution. By injecting a red-detuned cooling laser, we optically cool all of the modes that we observe. The lowest effective temperature we achieve is Teff ≈ 1 K.

Applications of sub-wavelength grating mirrors in high-power lasers

Abstract A grating waveguide mirror (GWM) results from the combination of a waveguide and a sub-wavelength grating which lead, for given incidence conditions, to polarization and or wavelength filtering. In the present paper, we report on the application of such elements for the selection of the polarization (linear, radial, or azimuthal) as well as the narrowing, stabilizing and tuning of the emission spectrum of high-power lasers. Using a leaky-mode circular GWM, beams with radial and azimuthal polarization with output powers of up to 275 W and 145 W, respectively, could be extracted from a Yb:YAG thin-disk with optical efficiencies of 52.5% and 43%, respectively. In both cases, the GWM was composed of a highly reflective (HR) mirror and a sub-wavelength grating as the end-mirror of the resonator. Using a leaky-mode linear GWM operating under Littrow condition, beams with linear polarization and a narrow spectral bandwidth were obtained from a Yb:YAG thin-disk laser. In multimode operation, an output power of 325 W was achieved at an optical efficiency of 53.5%. In near-fundamental mode operation, 110 W was extracted at an optical efficiency of 36.2%. In this latter case, the spectral bandwidth was measured to be around 25 pm. Moreover, continuous wavelength tuning from 1007 to 1053 nm was demonstrated with our device.

Mid-infrared sub-wavelength grating mirror design: tolerance and influence of technologicalconstraints

High polarization selective Si/SiO2 mid-infrared sub-wavelength grating mirrors with large bandwidth adapted to VCSELintegration are compared. These mirrors have been automatically designed for operation at λ = 2.3 µm by an optimization algorithm which maximizes a specially defined quality factor. Severaltechnological constraints in relation to the grating manufacturing process havebeen imposed within the optimization algorithm and their impact on the opticalproperties of the mirror have been evaluated. Furthermore, through the tolerancecomputation of the different dimensions of the structure, the robustness with respect tofabrication errors has been tested. Finally, it appears that the increase of the opticalperformances of the mirror imposes a less tolerant design with severer technologicalconstraints, resulting in a more stringent control of the manufacturing process.

Optimized sub-wavelength grating mirror design for mid-infrared wavelength range

Several designs of sub-wavelength grating mirrors adapted to mid-infrared operation are reported with several percents of tolerance for the grating fabrication. These designs have been automatically optimized by the use of a genetic-based algorithm to maximize a quality factor defined to meet the requirements of a VCSEL cavity mirror. These mirrors are devoted to integration in VCSEL operating near λ=2.3 μm, with a large bandwidth, very high reflectivity coefficient for transverse magnetic mode only, polarization selectivity and a thickness as low as 2 μm.

A broad-band waveguide grating coupler with a subwavelength grating mirror

A new diffractive device for light coupling between a planar optical waveguide and free space is proposed. The device utilizes a second-order waveguide grating to diffract the fundamental waveguide mode into two free propagating beams and a subwavelength grating (SWG) mirror to combine the two free propagating beams into a single beam. The finite-difference time-domain (FDTD) simulations show that the SWG mirror improves the coupling efficiency of the waveguide fundamental mode into the single out-coupled beam from about 30% to 92%. A high efficiency (>90%) is predicted for a broad wavelength range of 1520-1580nm. The proposed device is compact (/spl sim/80 /spl mu/m in length) and it eliminates the need for blazing the waveguide grating.