We discuss a new concept of dielectric subwavelength grating leveraging high index contrast to manipulate light to achieve ultra broad band reflector, high-Q resonator, planar high numerical aperture lens and reflector, and hollow-core integrated optics.

High contrast gratings for integrated optoelectronics

We review recent advances in subwavelength high-index-contrast gratings (HCGs) and a variety of applications in optoelectronic devices, including vertical-cavity surface-emitting lasers (VCSELs), tunable VCSELs, high-Q optical resonators, and low-loss hollow-core waveguides (HWs). HCGs can serve as broadband (Delta lambda/lambda ~ 35%), high-reflectivity (>99%) mirrors for surface-normal incident light, which is useful to replace conventional distributed Bragg reflectors in optical devices. HCGs can also be designed as high-Q resonators with output coupling in the surface-normal direction. Finally, we discuss a novel design of HCG as shallow angle reflectors and HWs.

High-Index-Contrast Grating (HCG) and Its Applications in Optoelectronic Devices

Techniques for enhancing the absorption of photons in semiconductors with the use of microstructures are described. The microstructures, such as pillars and/or holes, effectively increase the effective absorption length resulting in a greater absorption of the photons. Using microstructures for absorption enhancement for silicon photodiodes and silicon avalanche photodiodes can result in bandwidths in excess of 10 Gb/s at photons with wavelengths of 850 nm, and with quantum efficiencies of approximately 90% or more.

Microstructure enhanced absorption photosensitive devices

A new concept of dielectric subwavelength grating has emerged. This grating leverages a high contrast in refractive indices for the grating medium and its surroundings. We will discuss how high-index-contrast grating (HCG) can manipulate light to achieve various extraordinary properties. We will discuss various designs to yield broadband, high-reflectivity mirrors for light incident in surface-normal direction and at a glancing angle, ultra high-Q resonators with surface-normal output, planar high focusing power reflectors and lenses, and ultralow loss hollow-core waveguides. The HCG will be a new, promising platform for integrated optics with applications for lasers, filters, waveguides, sensors and detectors.

https://iopscience.iop.org/article/10.1088/0268-1242/26/1/014043/pdf

High-contrast gratings as a new platform for integrated optoelectronics

An optical waveguide is constructed so as to comprise a non-solid core layer surrounded by a solid-state material and a nanopore or micropore in fluid communication with the core. The non-solid core layer has an index of refraction which is lower than the index of refraction of the surrounding solid-state material, and light can be transmitted with low loss through the non-solid core layer. In an exemplary application, the non-solid core layer comprises a sample material whose light transmission, absorption, and/or interference characteristics are to be measured. In addition, a perpendicular waveguide portion may be included for use in injecting light into the core for measuring fluorescence characteristics associated with the sample material. Most preferably, the optical waveguide is generally structured as an anti-resonant reflecting optical waveguide (ARROW), which comprises a Fabry-Perot reflector adjacent to the core layer, whereby light is substantially prevented from leaking out of said core in a transverse direction.

Integrated sensor with electrical and optical single molecule sensitivity

We propose a hollow optical waveguide with metal coating or dielectric multilayer coating to achieve sufficient reflectivity at guiding walls. Low-loss and polarization-insensitive propagation characteristics are predicted. The propagation constant is independent of the temperature, resulting in temperature-insensitive photonic waveguide devices, such as optical filters and grating optical demultiplexers. We demonstrate a hollow optical waveguide with metal-coated walls on a GaAs substrate, which was fabricated using dry etching. The propagation loss including the coupling loss with an input fiber was 2.6 dB/cm and 7.3 dB/cm for transverse electric (TE) mode and transverse magnetic (TM) mode, respectively.

https://iopscience.iop.org/article/10.1143/JJAP.40.L688/pdf

Hollow Optical Waveguide for Temperature-Insensitive 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.

Modeling and Fabrication of Hollow Optical Waveguide for Photonic Integrated Circuits

We propose novel micromachined tunable waveguide devices based on hollow optical waveguides. The combination of hollow waveguides and mechanical movable elements gives us a large change in a propagation constant of guided waves in a hollow waveguides. We fabricated a three-dimensional (3-D) hollow waveguide and experimentally demonstrated the change of the propagation constant in the 3-D hollow waveguide with a variable air core. We observed the wavelength shift of 1.8 nm in a hollow waveguide resonator with a displacement of 6 /spl mu/m in an air core.

Novel phase-tunable three-dimensional hollow waveguides with variable air core

We present the design and the fabrication of low-propagation-loss and polarization-insensitive hollow waveguides with GaAs/AlAs semiconductor multilayer mirrors for widely tunable waveguide devices. We achieved a low propagation loss of less than 0.2 dB/cm for the transverse electric (TE) mode using 32-GaAs/AlAs-pair multilayers. The addition of a phase-control layer to the top surface of the mirrors results in a low polarization-dependent propagation loss of less than 0.2 dB/cm.

Low-Loss and Polarization-Insensitive Semiconductor Hollow Waveguide with GaAs/AlAs Multi-Layer Mirrors

We present the core thickness dependence of the propagation loss and the polarization dependence loss (PDL) of hollow waveguides of various air core thicknesses. The addition of phase-control layers to GaAs/AlAs multilayer mirrors enables us to reduce the PDL by one order of magnitude. The propagation loss and the PDL of a 5 µm air core hollow waveguide are 2.8 dB/cm and 1.7 dB/cm, respectively, which are currently limited by the reflectivity (0.998) of the GaAs/AlAs multilayer mirrors.

Toru Miura

Papers

Hollow Optical Waveguide for Temperature-Insensitive Photonic Integrated Circuits

Modeling and Fabrication of Hollow Optical Waveguide for Photonic Integrated Circuits

Novel phase-tunable three-dimensional hollow waveguides with variable air core

Low-Loss and Polarization-Insensitive Semiconductor Hollow Waveguide with GaAs/AlAs Multi-Layer Mirrors

Air Core Thickness Dependence of Propagation Loss of Slab Hollow Waveguide