A very large transmission, 20%, of light through a nano metallic slit bordered by both nano trenches and bumps has been demonstrated theoretically. The trenches bordering the nano slit, are used to excite free-space light into surface waves, while the bumps bordering the trenches are used to confine surface wave leakage. Over 50% of the escaping surface waves can be reclaimed by using a pair of bumps with a reflectivity larger than 99%. As a result, the transmission of a trench-surrounded slit bordered by a pair of bumps can be enhanced 1.5 fold.
In this paper, silicon-based micro and subwavelength optical elements based on a free-standing silicon nitride (SiN<sub>x</sub>)
membrane are achieved. These elements, including gratings, microlenses, and holographic optical elements (HOEs), are
designed and used within the visible and infrared regions. These devices can be used as collimators, reflectors, and
wavelength-dependent filters with advantages of simple structure, high efficiency and feasibility to integrate with other
elements into a micro-system chip. In order to demonstrate the advantage of micro-optics of free-standing SiN<sub>x</sub>
membrane type in integration, a miniaturized optical pickup head module based on a stacked micro-optical system is
developed. This module consisted of a laser diode, a reflector, a grating, a holographic optical element, and some
aspherical Fresnel lenses. The novel microoptical system can overcome the problems encountered in other microoptical
systems such as off-axis aberration, lower optical efficiency or durability, integration and even in fabrication. A focal
spot with a FWHM diameter of 3.3 μm is obtained while the diffraction limited full-width at half-maximum (FWHM) is
0.7 μm. To extend the advantage of micro-optics of free-standing SiNx membrane, the subwavelength optical elements
base on guided-mode resonance is also developed. With various Si-based structures, the filter possesses numerous
properties such as variable bandwidths, low sideband, flattop, and etc. They are also applied as biosensors to detect the
hybridization process of bio reaction for their high sensitivity. The results show that micro and subwavelength optical
elements fabricated on Si-based material will be a candidate for emerging silicon micro-photonics.
A hybrid grism lens, which integrates an off-axis diffractive grating and an on-axis refractive lens onto a prism structure, is developed. The proposed grism lens can simplify the setup of grating-based wavelength-division multiplexing (WDM) device owing to the dual-functional characters combined within only one element. The 100-GHz dense WDM (DWDM) device based on the grism lens is designed with an insertion loss of 2.91±0.53 dB and a crosstalk of 58.02 dB. The tolerance analysis, the allowable grating tilt angle of ±0.5 deg and fiber displacement of ±1 µm, shows that the proposed structure could be practically applied to the grating-based demultiplexers.
We develop a miniaturized optical signal pickup module, with a working wavelength of 650 nm, and an image numerical aperture (NA) of 0.6, comprised of several SiNX optical phase elements on stacked Si substrates, for use in optical storage systems. The optical module, which is optical-on-axis and transmissible in both visible and infrared ranges, is designed to include not only a light source, but also diffractive optical elements (DOEs), which can be made with micro-optoelectromechanical systems (MOEMS) technology. Its optical operation is simulated by ray tracing to optimize the spot size (~0.6 µm) focused on the disk by adjusting the tolerance of each element in the alignment. All the Si-based transmission optical elements are fabricated and stacked by self-alignment bonding to reduce the tolerance of the assembled system. We obtain a circular focused spot when the full-width at half maximum (FWHM) of the zero-order beam is 3.1 µm; the diffraction limited spot size on the optical disk is 0.7 µm.
We developed a new optical element which integrates an off-axis diffractive grating and an on-axis refractive lens surface in a prism. With this optical element, the alignment tolerance can be improved by manufacturing technology of the grating based WDM device and is practicable for mass production. An 100-GHz 16-channel DWDM device which includes this optical element has been designed. Ray tracing and beam propagation method (BPM) simulations showed good performance on the insertion loss of 2.91±0.53dB and the adjacent cross talk of 58.02dB. The tolerance discussion for this DWDM device shows that this optical element could be practically achieved by either injection molding or the hot embossing method.
The hydrogenated Silicon nitride film is well developed to form a passivation layer for non-volatile memory devices. It has many superior chemical, electrical, and mechanical properties. In addition, it also has excellent optical properties. It is transparent in UV and DUV range, with a high refractive index of about 1.7~2. Owing to its superior mechanical and optical properties, we used a hydrogenated silicon nitride (SiN<sub>X</sub>H<sub>Y</sub>) membrane as an optical phase element. By using e-beam lithography, we demonstrate on feasibility for the fabrication of subwavelength optical elements, such as waveplate, polarizer, and polarized beam splitter on a silicon-based low stress SiN<sub>X</sub>H<sub>Y</sub> membrane for the UV region applications. An SiN<sub>X</sub>H<sub>Y</sub> film was deposited by plasma enhanced chemical vapor deposition (PECVD) and the free- standing membrane is formed by KOH silicon backside etching, from which substrate materials are removed. The membrane's morphology and geometries of subwavelength optical elements were verified by means of an scanning electron microscope (SEM), and the optical performance characteristics of these subwavelength optical elements are shown. The experimental datas agree well with theoretical predictions.
In this paper, fabrication an optical filter based on guided-mode resonance (GMR) effect in a silicon nitride (SiNx) membrane by silicon bulk micromachining technologies is demonstrated. Such a filter has advantages of simple structure, high efficiency and it is potential to be integrated with other developed optoelectronic elements into an integrated micro systems. The design consideration, fabrication procedures and measured spectral response are shown in this paper.
The optical transmission and distribution through a subwavelength slit on a tapered metallic substrate was investigated. By using a 45° tapered structure, 6 times larger transmission enhancement was achieved compared with a traditional metallic plate structure because of the asymmetric excited surface waves and the matching of propagation constants between the surface waves and slit waveguide. In addition, a focus beam was obtained by patterning surface corrugations in the exit plane. By tuning the period of the surface corrugations, we were able to adjust the focal length with a spot size smaller than the diffraction limit. The focal point can be kept about 0.6μm with a focal length from 0.5μm to 2.5μm for a grating period from 0.5μm to 0.6μm.
For the detection of molecular interaction, a novel approach of the guided-mode resonance (GMR) spectroscopy identifies molecules via specific bindings with their ligands immobilized on the grating surface is presented. The structure of GMR device generally consists of two stages -- upper grating layer and waveguide layer. When the wide-band light illuminating, the GMR device inhibits on a specific resonant narrow-band of wavelength, and allows for other wavelength to transmit. The specific resonant narrow-band of wavelength results in the diffraction of the incident wide-band wave and the selection in the waveguide layer. This is very useful in highly sensitive measurement, especially for the variations in the refractive index of bulk media, and for the monitoring of variations in the thickness of thin film. In the simulation, one <i>Si</i><sub>3</sub><i>N</i><sub>4</sub> (<i>n</i>=2) GMR device is designed. When the wavelength of the illumination ranges from 1520nm to 1620nm, the resonant peak wavelength will shift 0.03nm as per
1nm bio-layer (<i>n</i><sub><i>bio</i></sub> 1.3) has been attached on. Finally, on the basis of the theoretical analysis, the optimization of a spectral GMR sensor in terms of the operation wavelength has been carried out.
We have developed a novel stacked silicon-based microoptical system, which is optical-on-axis and transmissible in both visible and infrared ranges. By using the new microoptical system techniques, we fabricated a miniaturized optical pickup head module. This optical pickup head consisted of a 650nm laser diode, a 45 degrees silicon reflector, a grating, a holographic optical element, and some aspherical Fresnel lenses. These optical phase elements fabricated on a SiNx membrane were free-standing on Si chips. Each element was then stacked by chip bonding. We could obtain a circular focusing spot on the optical disc as small as 3.1um.
We have proposed a miniaturized optical signal pickup module comprised of several SiNX membrane devices on stacked Si substrates for use in optical storage system. The optical module was designed to include not only light sources and detectors, but also the diffractive optical elements (DOEs), which can be made with microoptoelectromechanical systems (MOEMS) technology. Its optical operation was simulated by ray-tracing to have an optimized spot size (~0.6μm) focused on the disk with setting the tolerance of each element for the alignment. All these Si-based transmission optical elements were fabricated and can be stacked by self-alignment bonding for system assembly.
Silicon nitride (SiN<sub>X</sub>) film is a commonly used material in silicon technology. In addition, it has excellent optical properties. It is transparent in both the UV and visible range, with a high refractive index of about 1.7~2. Owing to its superior mechanical and optical properties, we used a silicon nitride membrane as an optical phase element. We will fabricate nano-structured diffractive optical elements, such as wave-plate, polarizer, and polarized beam splitter on SiNXHY membrane by e-beam lithography for the UV-visible regime applications. The SiNXHY membranes were made from SiN<sub>X</sub>H<sub>Y</sub> films deposited by an plasma enhanced chemical vapor deposition (PECVD) as an alternative method for low stress membrane fabrication used in UV-visible transmittance. The stress of silicon nitride film showed a change from compressive to tensile with increasing working pressure during film deposition. The UV-visible transmittance of the free standing membrane was measured, which showed that UV light is transparent at wavelength as short as 240nm. We will show the feasibility to fabricate nano-structured diffractive optical elements on the SiN<sub>X</sub>H<sub>Y</sub> membrane combined with microoptoelectromechanical systems (MOEMS) technology for the application in the UV-visible regimes.
An out-of-plane guided-mode resonance (GMR) filter on a single Si chip using a two-layer polysilicon surface micromachining process was proposed. To the best of our knowledge, this is the first time that a monolithic optical filter has been integrated on a silicon microoptical bench. This device can be used as a bi-directional transceiver filter. The extinction ratio between 1550nm and 1310nm could be as low as 40dB and the channel passband at 1550nm was 20nm.