This PDF file contains the front matter associated with SPIE Proceedings Volume 8270, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
Conceptual approaches used to analyse optical properties of surface-addressable photonic crystal membrane
(PCM) resonators will be briefly presented. It will be pointed out that these photonic structures can also be
referred to as high-contrast gratings (HCGs) and that bridges can be made with other approaches proposed in the
recent literature to analyse the latter. It will be demonstrated that high reflection mirrors, with arbitrarily
adjustable bandwidth, can be designed along the PCM approach, where leaky wave-guided slow Bloch modes
play the primary role. Implementation examples of such reflectors are presented, with a special emphasis on the
use of large bandwidth PCM reflector: vertical-cavity surface-emitting lasers (VCSELs) using hybrid III-V / Si
microcavities, based on double PCM reflectors, have been recently fabricated. These devices are meant to be
compatible with their heterogeneous integration on complementary metal-oxide-silicon (CMOS). It will be
shown that the operation of this new class of VCSEL is based on hybrid optical modes, whose properties can be
fully monitored by appropriate design of the PCM reflectors. For example, specific architectures can be targeted
for laser emission either in free space, or into silicon waveguides. The latest achievements in technological
processing, optical mode engineering and laser performances will be presented as well.
High contrast gratings (HCG) have various unique features such as broadband high reflections, high-Q resonance,
spatial control of optical phase and so on. We focus on the angular dependence of HCG, which can be managed by
designing grating parameters. The angular dependence of HCG is much larger than that of conventional quarter-wavelength
stack mirrors while keeping their broadband high reflections. The engineered angular dependence can be
useful for spatial mode MUX/DEMUX devices. A possibility of spatial mode demultiplexer based on HCG hollow
waveguides is suggested for use in optical interconnects with spatial mode multiplexing. Also, we discuss the transverse
mode control of HCG-loaded VCSELs.
We introduce concepts for direction selective transmission filters based on dielectric high-contrast gratings. The
devices act as angular bandpass filters at an incidence angle of 45° with a total transmission of 68% and a full
width at half maximum of 20°. Since the filters are based on a material combination of silicon and silicon dioxide
they provide an excellent compatibility to well established fabrication processes in semiconductor industry. The
results of measurements on fabricated samples are presented and the performance of the components is compared
to that of metallic gratings. It is found that the latter can basically provide similar filter properties, however the
feasible transmission efficiency is significantly lower than for the dielectric gratings. The presented configurations
are applicable in the field of sensors and detectors.
Nanoimprint lithography is a powerful tool for making large area sub-wavelength scale optical devices with high-throughput
fabrication. We developed a thermal nanoimprint lithography process for making sub-wavelength HCG
patterns on an SOI substrate. A vertical etching profile and a smooth etched surface, which meet the requirements for Si
based HCG structure, were obtained. We fabricated large area (1cm x 1cm) HCG with good uniformity in the entire
sample. The clear angular dependence of the reflectivity of Si-HCG can be seen, which is in good agreement with the
modeling result. The engineered angular dependence of HCG could be useful for the mode control of VCSELs and
spatial mode multiplexers.
We present a new type of Si-based, metastructure, hollow-core waveguide that has highly desirable "slow-light" and
low-loss properties for providing time-delays or high-Q cavities in chip-scale integrated OE circuits. This waveguide has
high contrast grating (HCG) metastructures as the 4 claddings/walls of a squared hollow-core structure. We have
successfully fabricated this 3-D metastructure waveguide using a new nano-fabrication techniques including one selfaligned,
cycled, modified Bosch etch process. Our computational modeling indicates that there is a slow-light region
with very little propagation loss. We will report our preliminary experimental waveguide test results for propagation loss
and group velocity.
We propose a novel hollow-core slow light waveguide using high contrast grating (HCG). Light propagates in air along
a path bounded by two HCG layers. A strong interaction between the light and the HCG leads to a large group index,
and thus the slow light effect. Waveguide loss and group index can be optimized separately by tuning the HCG and
waveguide parameters. High performance slow light is obtained with <0.1 dB/cm loss, >120 group index and >120 GHz
Through a fully analytical model [Phys. Rev. B 78, 245108 (2008)], we investigate the impact of several disorder models
on backscattering losses in photonic crystal waveguides. To evaluate their relative relevance, we compare the predictions
with loss measurements. The comparison suggests that a long-range disorder at the scale of every hole has to be
considered in disorder model, in addition to the more classical hole surface roughness.
In this talk, novel vertical-cavity laser structure consisting of a dielectric Bragg reflector, a III-V active region,
and a high-index-contrast grating made in the Si layer of a silicon-on-insulator (SOI) wafer will be presented. In
the Si light source version of this laser structure, the SOI grating works as a highly-reflective mirror as well as
routes light into a Si in-plane output waveguide connected to the grating. In the vertical-cavity surface-emitting
laser (VCSEL) version, there is no in-plane output waveguide connected to the grating. Thus, light is vertically
emitted through the Bragg reflector. Numerical simulations show that both the silicon light source and the
VCSEL exploiting SOI grating mirrors have superior performances, compared to existing silicon light sources
and long wavelength VCSELs. These devices are highly adequate for chip-level optical interconnects as well as
conventional short-distance optical connections. In the talk, device physics will be discussed in detail.
High-index-contrast grating mirrors featuring beam steering abilities for the transmitted beam as well as high reflectivity
over a broad bandwidth are suggested. Gratings designed to provide control over the wave front of the transmitted beam
are numerically investigated. The proposed structures are then fabricated for experimental characterization. The
measurements performed show the beam steering ability of the suggested HCG designs and are also in good agreement
with the theoretical predictions. General design rules to engineer these HCG structures for different applications are
derived. These grating mirrors would have a significant impact on low cost laser sources fabrication, since a more
efficient integration of optoelectronic modules can be achieved by avoiding expensive external lens systems.
In this work we present a wire grid polarizer with a working range down to 300 nm based on an amorphous silicon
grating. For the fabrication of gratings with periods of 120 nm and 140 nm electron beam lithography and ICP
etching were used. Furthermore the influence of the grating period on the optical properties was investigated.
The measured maximum value of the extinction ratio for a period of 140 nm and 120 nm is 177 at a wavelength
of 418 nm and 324 at a wavelength of 394 nm, respectively.
A challenge to the past, an optical phased array for far field beam steering with varied High-Contrast Grating (HCG)
waveguides is proposed. For one-dimensional beam steering, the laser light is split into N co-directional HCG
waveguides. Simulations and calculations shows slow light waveguide output tunable phase with varied HCG
dimensions or index. The far field beam steering effect is presented and will be seen clearly by add array element
We present a novel form of hollow-core waveguiding that enables chip-scale integration. Light propagates in air along a
zig-zag path between very highly-reflective Si metastructures comprised of a single layer of sub-wavelength high-contrast
gratings (HCGs) without the aid of sidewalls. Top and bottom subwavelength HCGs separated by 9um of air
and with periodicity perpendicular to the propagation of light reflect light at shallow angles with extremely low loss.
The HCGs are patterned on SOI wafers with 340 nm-thick Si device layers engraved in a single etch step, and have been
measured to have a 0.37 dB/cm propagation loss. Our work demonstrates the light-guiding properties of HCG hollow-core
waveguides with a novel form of lateral beam confinement that uses subtle reflection phase changes between core
and cladding HCG regions capable of bending light around 30 mm radius-of-curvature tracks.
We propose a novel vertical optical coupler using subwavelength high contrast grating. The
surface normal incidence light can be coupled into the in-plane waveguide with peak efficiency
of 92% over a broad wavelength range. Such structure can be also designed as the in-plane
reflector or in-plane to vertical coupler. The reflectivity for waveguide propagation mode is 97.5%
and the coupling efficiency is 96%, respectively.
On-chip laser beam tracking finds innumerable applications. Popularly adopted quadrant photodiodes can only detect
laser beam's angle variation up to 0.2° reliably. In this paper, a novel angle detector is designed based on grating
coupling. It consists of a grating layer on top of a silicon-on-insulator slab waveguide. The incident light is coupled into
guided modes within the waveguide via the grating layer, and then, the incident light's angle can be determined by
reading the outputs of light detectors within the waveguide. Performance of the laser angle detector in this paper is
demonstrated by full-wave finite-difference-time-domain simulations. Numerical results show that, the detectable angle
range can be adjusted by several design parameters and can reach [-4°, 4°]. The device structure in this paper can be
straightforwardly extended to two-dimensional photonic crystal configurations.
A scheme of applying high contrast grating hollow waveguide (HCG-HW) to optical phased array (OPA) as the
transmission waveguide and phase shifter is proposed. The phase shift with varied HCG-HW dimensions is deduced in a
theoretical approach and demonstrated by the simulation results. Beam steering in one direction is done by varying the
wavelength. A phase shift range of 18.7 rad and the beam angle shift to 12.62° with varied wavelengths are presented.
We report on novel concepts for reflective diffractive elements based on high-contrast gratings. To demonstrate
the possibilities for such devices reflective cavity couplers with three output ports are investigated. A diffracting
period is superposed to a highly reflective subwavelength grating in order to realize diffractive elements. This
superposition can be realized with a periodic depth, fill factor or period modulation of the reflector. Further, to
limit the total transmission of the device it is necessary to enhance its angular tolerance. We discuss different
approaches in order to realize this increased reflectivity in broad range of the angular spectrum. The contribution
focuses on the material combination silicon-silica, but the presented concepts also hold for other material
combinations with large index contrast and even for monolithic silicon structures.
A new planar light concentrator design is proposed by using unique diffraction properties of high-contrast
subwavelength gratings (HCGs). HCGs have the ability to diffract the incoming light at steep angles with very high
efficiency. By integrating the HCGs on top of planar glass substrates, light can be guided in the glass leading to high
concentration at the edges. Finite difference time domain simulation results show that concentration ratio close to 50 can
be achieved by optimizing the grating parameters. These planar light concentrators find application in various areas
including concentrated solar power, light pipes and spectrum splitters.
In high temperature and vacuum applications, for which heat transfer is predominantly by radiation, the material's
surface texture is of substantial importance. Control of thermal emission is of crucial concern in the design of infrared
sources, in electronic chip coolants, in high-efficiency photovoltaic cells, and in solar energy conversion. Thermal
emission has been shown to be modified by utilizing the high density of states of surface waves (surface plasmon
polaritons and surface phonon polaritons) and their long-range propagation. We present subwavelength structures -
metastructures supporting surface waves for obtaining polarization manipulation of thermal emission, extraordinary
coherent thermal radiation, bandgap in the spectral emission, and a broadband infrared absorption. A spin-dependent
dispersion splitting was obtained in a structure consisting of a coupled thermal antenna array. The effect is due to a spinorbit
interaction resulting from the dynamics of the surface waves propagating along the structure whose local anisotropy
axis is rotated in space. The dispersion splitting due to the spin-orbit coupling is also known as the key feature in such
remarkable effects as the Rashba splitting and the spin-Hall effect, which indicates the generic nature of the discussed
phenomenon. The observation of the spin-symmetry breaking in thermal radiation paves the way to manipulate
spontaneous emission with the photons' intrinsic degree of freedom and provides the basis for future spinoptics devices.
Low-loss waveguides integrated on a silicon substrate are essential components in the design and
fabrication of photonic circuits. For this application, a wide operational bandwidth - from visible to
infrared wavelengths - is critical. Previous research has yielded waveguides made with various materials
and geometries. Several of these devices have achieved low, <0.1dB/cm loss in either the visible or the
near-IR. However, to obtain effective confinement of light from the visible through the near-IR, it is
necessary to develop waveguides which have near-constant loss and minimal non-linear effects across the
entire wavelength range.
To overcome this challenge, we have developed novel silica on silicon waveguides fabricated
using conventional lithographic techniques and CO2 laser reflow. The entire waveguide is elevated above
the higher refractive index silicon substrate, creating an isolated, air-clad waveguide. The cylindrical
waveguide's loss was determined by coupling light from 658nm, 980nm, and 1550nm lasers into the
waveguide using lensed optical fibers. Due to the inherently low material loss of silica and the isolation
from the silicon substrate, the device has low optical loss (0.7-0.9dB/cm) and linear behavior across the
entire wavelength, polarization, and input power ranges studied. These on-chip waveguides will benefit
many applications, including biodetection and integrated photonics.
Optical beam splitters form a fundamental component in integrated optical systems, performing as modulators,
interferometers and (de)multiplexers. While silica is a desirable material, because of its low non-linear susceptibility, it is
extremely challenging to achieve the requisite core-clad refractive index contrast. In this work, silica splitters with an
effective refractive index difference of 25% between the core and clad is demonstrated. The splitter can divide power
evenly with low crosstalk from 1520 to 1630nm. In addition, the splitting ratio doesn't change and the output power
increases linearly with the input power, which indicates a low susceptibility to thermal effects. The splitter's polarization
independent behavior is also verified.
Proc. SPIE 8270, Tuning the reflectivity of high-contrast gratings based on silicon and silica by means of wet etching with hydrofluoric acid, 82700U (23 February 2012); https://doi.org/10.1117/12.908240
We report on experimental etching techniques to trim the efficiency of high-contrast gratings based on silicon and
silica. We show that the resonance wavelength and hence the reflectivity can be tuned by means of selectively
etching the silica grating. In order to realize a well-defined adjustment of the grating profiles the etching rates of
silica layers with hydrofluoric acid were determined. Coatings deposited by different techniques such as electron-beam
evaporation, ion plating and thermal oxidation are compared and the influence of structuration on the
etching is investigated, as well. This work basically helps to improve the maximum reflectivity that can be
realized with these high-contrast reflectors and tune the resonance to a required wavelength.