A symmetrically stacked structure [(a-Si:H(n+)/a-Si:H(i)/CZ wafer (n)/a-Si:H(i)/a-Si:H(n+)] was used to optimize the growth process conditions of the n-type hydrogenated amorphous silicon [a-Si:H(n+)] thin films. Here a-Si:H(n+) film was used as back surface field (BSF) layer for the silicon heterojunction solar cell and all stacked films were prepared by conventional radio-frequency plasma-enhanced chemical vapor deposition. The characterizations of the effective carrier lifetime (τeff), electrical and structural properties, as well as correlation with the hydrogen dilution ratio (R=H2/SiH4) were systematically discussed with the emphasis on the effectiveness of the passivation layer using the lifetime tester, spectroscopic ellipsometry, and hall measurement. High quality of a stacked BSF layer (intrinsic/n-type a-Si:H layer) with effective carrier lifetime of 1.8 ms can be consistently obtained. This improved passivation layer can be primarily attributed to the synergy of chemical and field effect to significantly reduce the surface recombination.
We investigated the influence of free-standing GaN (FS-GaN) substrates on the performance of ultraviolet light-emitting-diodes (UV-LEDs) grown on top by atmospheric pressure metal-organic chemical vapor deposition. High-resolution double-crystal x-ray diffraction (HRDCXD) analysis demonstrated high-order satellite peaks and clear fringes between them for UV-LEDs grown on the FS-GaN substrate, from which the interface roughness was estimated. In addition, the full width at half maximum of the HRDCXD rocking curve in the (0002) and the (101¯2) reflections were reduced to below 90 arc sec. The Raman results indicated that the GaN-based epilayer of strain free was grown. Additionally, the effect of the FS-GaN substrate on the crystal quality of the UV-LEDs was examined in detail by transmission electron microscopy (TEM). The TEM characterizations revealed no defects and V-pits were found in the scanned area. Based on the results mentioned above, the light output power of UV-LEDs on the FS-GaN substrate can be enhanced drastically by 80% and 90% at 20 and 100 mA, respectively. Furthermore, an ultralow efficiency degradation of about 3% can be obtained for the UV-LEDs on the FS-GaN substrate at a high injection current. The use of an FS-GaN substrate is suggested to be effective for improving the emission efficiency and droop of UV-LEDs grown thereon.
We reported the defects and optical characterizations of the ultraviolet light-emitting diodes grown on free-standing GaN
substrate (FS-GaN) and sapphire. Cross-sectional transmission electron microscopy (TEM) images showed that the total
defect densities of grown UV LEDs on FS-GaN and sapphire including edge, screw and mixed type were 3.6×106 cm-2 and 5.5×108 cm-2. When substrate of UV LEDs was changed from sapphire to FS-GaN, it can be clearly found that the crystallography of GaN epilayers was drastically different from that GaN epilayers on sapphire. Besides, the microstructures or indium clustering can be not observed at UV LEDs on FS-GaN from TEM measurement. The internal quantum efficiency of UVLEDs on FS-GaN and sapphire were 34.8 % and 39.4 % respectively, which attributed to
indium clustering in multi-layers quantum wells (MQWs) of UV LEDs on sapphire. The relationship between indiumclustering
and efficiency droop were investigated by temperature-dependent electroluminescence (TDEL) measurements.
In this study, a metal assisted guide mode resonance device for bioanalytical applications is proposed. The particular
spectrum inversion property and its resonance mechanism are discussed. The metal assisted guided mode resonance
eliminates evanescent wave distributed in substrate and provides a strongly asymmetric modal profile; the evanescent
wave is one fold enhanced in top medium. The intrinsic bulk sensitivity achieves 337.5 in a fundamental TM mode
resonating at 800nm with 1st diffraction angle.
An optical fiber sensor based on evanescent wave sensing and excitation light resonance using a pair of optical reflectors
adjacent to two ends of the optical fiber is presented. Excitation light is coupled into the fiber optical sensor through a
hole in the first reflector. The excitation light starts to resonate between the reflectors, and results in the amplification of
the fluorescent signal, which is generated by the excitation of the analyte binding to the surface of the active fiber
sensing area. This device was successfully demonstrated in achieving over 600% amplification in the output signal. This
design provides a simple and efficient method in improving the S/N and the sensitivity of the optical fiber evanescent
wave sensor over the traditional approach.
In this Letter, the identification device disclosed in the present invention is comprised of: a carrier
and a plurality of pseudo-pixels; wherein each of the plural pseudo-pixels is formed on the carrier
and is further comprised of at least a light grating composed of a plurality of light grids. In a
preferred aspect, each of the plural light grids is formed on the carrier while spacing from each
other by an interval ranged between 50nm and 900nm. As the aforesaid identification device can
present specific colors and patterns while it is being viewed by naked eye with respect to a
specific viewing angle, the identification device is preferred for security and anti-counterfeit
applications since the specific colors and patterns will become invisible when it is viewed while
deviating from the specific viewing angle.
We report the design, fabrication, and experimental demonstration of active narrowband multiple wavelength filters in
aperiodically poled lithium niobate (APLN) crystals. We obtained the simultaneous transmission of 8 ITU standard
wavelengths with transmittance of >90% (~100% in design) and a bandwidth of ~0.45 nm from a 5-cm long APLN Solctype
filter. Four peak-narrowed and highly sidelobe-suppressed second-harmonic generation (SHG) signals of four
telecom wavelengths from a monolithic LiNbO3 crystal cascading a 1-cm long APLN wavelength filter and a 1-cm long
APLN wavelength converter was also obtained.
In this paper, the design of effective microprism based on the subwavelength periodic lattices is proposed. The
microprism is realized by using a two-dimensional photonic crystal (PhC) structure with a periodic lattice of air-holes.
In order to behave as a homogeneous and isotropic microprism, the PhC structure with a hexagonal lattice should be
operated in the low frequency. By monolithically integrating the effective microprism in the bending area of an optical
waveguide, its wavefront of eigenmode could be tilted correctly to suppress the radiation loss in wide-angle bent
waveguides. In order to demonstrate the feasibility of proposed microprism for low-index-contrast waveguides, an
example of bent waveguide with the eigenmode nearly compatible to the single mode fiber is adopted to design the PhC
microprism. The transmission efficiency as high as 92% for the proposed structure with the bending angle of 12.96° and
the bending radius of 89.09 μm is achieved.
In this paper, the guide-mode resonance (GMR) devices based on a suspended membrane structure is designed and
experimentally demonstrated. The presented membrane structure possesses a simple structure for resonance excitation
and is capable of improving the spectral response. The results of resonance excitation, improving the sideband and low
oscillatory spectrum are presented. Due to the utilization of silicon-based materials, the proposed filter is also potential
candidates to be integrated with other optoelectronic devices for further applications.
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 (SiNx)
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 SiNx
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.
This study will discuss the heat dissipation effect of light emitting diode (LED) device applied a commercial miniature heat pipe (MHP). For lowering the thermal resistance of LED, the MHP can reduce the working temperature and raise the allowable input power of LED chip obviously. By comparing with a copper rod, the LED temperature was decreased about 19% at 1.59W input power and the LED power was increased about 43% under 118°C chip temperature. On the other hand, the thermal resistance of LED also can be reduced by using a thinner slug. Moreover, the results showed that the thermal spreading effect was significant. The MHP could be used to avoid the hot spot of LED packaging due to its excellent heat spreading property. Simultaneously, a LED thermal simulation was carried out to verify the optimum value of slug thickness.
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 (SiNXHY) 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 SiNXHY membrane for the UV region applications. An SiNXHY 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 Si3N4 (n=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 (nbio 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 (SiNX) 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 SiNXHY 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 SiNXHY 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.
We focus on a photorefractive response under the influence of temperature in conjunction with reduction. A series of reduced BaTiO3:Rh crystals is made. Their optical absorptions, dark decays, and light-induced decays are investigated. The temperature-dependent dark decay and light-induced decay are performed by an argon ion laser operated at 514.5 nm. The experimental results show that the photorefractive response can be improved by reduction in cooperation with the elevation of temperature. For different types of Rh-doped barium titanate crystals, the elevation of temperature has different influences in their photorefractive responses. The sample reduced at 10–14 atm has the best response of 15 ms at 100°C.
Optical elements, such as grating, holographic optical element and Fresnel lens, are made on the SiN membrane. The SiN film was deposited on the silicon wafer by low pressure chemical vapor deposition (LPCVD). Its advantages include the high transmission efficiency, light weight, and easy packaging for the Si-based optical pickup head.
Nominally undoped BaTiO3 crystals, processed in atmospheres of various oxygen partial pressure at 900 degree(s)C and 1000 degree(s)C, respectively, were fabricated and systematically investigated. The photorefractive properties are sequentially controlled by the factor from dark decay, deep/shallow trap, deep/shallow trap with hole/electron competition to dark conductivity, as the oxygen partial pressure is reduced. The trend is similar for both of the processing temperature, however, the compensation point is shifted about three of oxygen partial pressure. This can be attributed to a higher oxygen vacancy concentration st higher processing temperature.
We report that two beam coupling and response time of reduced BaTiO3:Rh at wavelengths of 514 nm and 633 nm. For the as-grown, the carriers are holes for both of wavelengths of 514 nm and 633 nm. When reduced at the atmosphere of 10-10 atm oxygen partial pressure, the carrier is electron for wavelength of 514 nm, and hole for 633 nm. With higher reduction, the carriers are electrons for both of wavelengths. Two beam coupling gain is also dependent on the reduction level and incident wavelength. For the as-grown, the trap density is 23 by 1016 cm-3 for 514 nm and 15 by 1016 cm-3 for 633 nm. For the sample reduced at the atmosphere of 10-10 atm oxygen partial pressure, the trap density decreases and is 5 by 1016 cm-3 for 514 nm and 2 by 1016 cm-3 for 633 nm. With higher reduction, the trap density increases and is 12 by 1016 cm-3 for 514 nm and 5 by 1016 cm-3 for 633 nm.
We demonstrate a photorefractive incoherent-to-coherent optical converter using anisotropic self-diffraction (ASD) in BaTiO3. Only two writing beams are required in the spatial light modulator and no extra readout beam is required. The diffraction efficiency reaches 50 percent. The resolution diffracted image is 22.6 lp/mm with a 6.6 by 6.6 by 7 mm crystal. We can increase the resolution by using a thin crystal without expense of the diffraction efficiency because of the inherent high diffraction efficiency of ASD in BaTiO3.
As for our knowledge, a simplest real-time system for measuring dynamic optical phase perturbation is proposed and demonstrated. In this system a 1% weight Fe:LiNbO3 is used to record the self-interference grating by the incident light. The interferometer is a new kind of double-exposure one. The speed of the interferometer is as fast as that of the dynamic phase perturbations.
The storage capacity of the random phase-coded volume hologram multiplexing which uses a ground glass as the random phase diffuser is reported. We found that the role of the ground glass imply the storage capacity of the random phase-coded multiplexing. From the experimental results, the tolerance of the position mismatch of the decoding ground glass is with a typical value of decades of micrometers, as reading an image. On the other hand, from the computer simulation, the signal-to-noise ratio of the readout images can be obtained by the pixel size of the ground glass. After mainly considering the tolerance of the position mismatch of the ground glass and the signal-to-noise ratio of the reconstructed image, the storage capacity of the random phase-coded multiplexing can be estimated.
An encoding method, random phase-coded multiplexing, was applied to the volume hologram multiplexing and demonstrated the recording of 100 holograms in a LiNbO3:0.01% Fe. The multiplexing method is simple because the encoding material is just a ground glass. A theory was also developed to interpret the properties of the method.
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