A multi-band pass filter array was proposed and designed for short wave infrared applications. The central wavelength of the multi-band pass filters are located about 905 nm, 950 nm, 1055 nm and 1550 nm. In the simulation of an optical interference band pass filter, high spectrum performance (high transmittance ratio between the pass band and stop band) relies on (1) the index gap between the selected high/low-index film materials, with a larger gap correlated to higher performance, and (2) sufficient repeated periods of high/low-index thin-film layers. When determining high and low refractive index materials, spectrum performance was improved by increasing repeated periods. Consequently, the total film thickness increases rapidly. In some cases, a thick total film thickness is difficult to process in practice, especially when incorporating photolithography liftoff. Actually the maximal thickness of the photoresist being able to liftoff will bound the total film thickness of the band pass filter. For the application of the short wave infrared with the wavelength range from 900nm to 1700nm, silicone was chosen as a high refractive index material. Different from other dielectric materials used in the visible range, silicone has a higher absorptance in the visible range opposite to higher transmission in the short wave infrared. In other words, designing band pass filters based on silicone as a high refractive index material film could not obtain a better spectrum performance than conventional high index materials like TiO2 or Ta2O5, but also its material cost would reduce about half compared to the total film thickness with the conventional material TiO2. Through the simulation and several experimental trials, the total film thickness below 4 um was practicable and reasonable. The fabrication of the filters was employed a dual electric gun deposition system with ion assisted deposition after the lithography process. Repeating four times of lithography and deposition process and black matrix coating, the optical device processes were completed.
The particular Graphene-Germanium-Graphene photodetector (GSG PD) is investigated in this research. Germanium has good absorption coefficient in near infrared such as 850 nm, 1310 nm and 1550 nm which are commonly used in optics communication. Generally, the metal electrode was utilized for photodetector and there were lots of light being loss. In recent years, graphene is found to be a good conductive film. It is a two-dimensional monolayer of sp2-bonded carbon atoms. In cases where synthesized by chemical vapor deposition (CVD), graphene is especially a promising candidate for transparent conductive films (TCFs) due to its exceptional electrical conductivity and high optical transmittance which is almost transparent in the wide wavelength range, especially including near infrared. Therefore, the higher photo current and responsivity of the device can be achieved.
In this investigation, interdigitated graphene electrodes are used on the devices with the purposes of a relatively easy process for high-speed devices and a comparable process for the integrated circuit. We used the n-type Germanium as the substrates for the absorption of photodetector and different layers of graphene as the interdigitated electrodes. The interdigitated graphene electrode is prepared by transferred the graphene which is grown by CVD on the substrate first and then pattern by O2 plasma. The most direct method of measuring the photo current is to be incident a laser source by fiber and give a DC bias then using KEITHLEY 2400 Source Meter to measure current from photodetectors. As the result of that, we can calculate the responsivity by formula.
Making progress in recent years, with the technology of the grating, the grating period can be reduced to shrink the size of the light coupler on a waveguide. The working wavelength of the light coupler can be in the range from the near-infrared to visible.
In this study , we used E-gun evaporation system with ion-beam-assisted deposition system to fabricate bottom cladding (SiO2), guiding layer (Ta2O5) and Distributed Bragg Reflector(DBR) of the waveguide on the silicon substrate. Electron-beam lithography is used to make sub-wavelength gratings and reflector grating on the planar waveguide which is a coupling device on the guiding layer. The best fabrication parameters were analyzed to deposit the film. The exposure and development times also influenced to fabricate the grating quality. The purpose is to reduce the device size and enhance coupling efficiency which maintain normal incidence of the light . We designed and developed the device using the Finite-Difference Time-Domain (FDTD) method. The grating period, depth, fill factor, film thickness, Distributed Bragg Reflector(DBR) numbers and reflector grating period have been discussed to enhance coupling efficiency and maintained normal incidence of the light. According to the simulation results, when the wavelength is 1300 nm, the coupling grating period is 720 nm and the Ta2O5 film is 460 nm with 360 nm of reflector grating period and 2 layers of Distributed Bragg Reflector, which had the optimum coupling efficiency and normal incidence angle. In the measurement, We successfully measured the TE wave coupling efficiency of the photoresist grating coupling device.
Due to the high attenuation in vitreous silica, acoustic attenuations in the THz regime are typically measured by
incoherent techniques such as Raman, neutron, and X-ray scattering. Here, we utilized multiple-quantum-well structures
to demonstrate acoustic spectroscopy of vitreous silica up to THz regime. The acoustic properties of silica thin films
prepared by chemical deposition methods were characterized in the sub-THz regime. This technique may be useful in
resolving debated issues relating to Boson peak around 1 THz.
Although the physics of structural color has been investigated, it remains a challenge to create artificial replicas of the natural photonic crystal structure. The concave multilayer replica of Papilio blumei butterflies is successfully fabricated by the following three main steps: self assembly of polystyrene spheres, deposition using an electron-beam gun, and inductively coupled plasma etching. The green iridescence of the wings of P. blumei is successfully reproduced.
Optical quality PMMA thin film layers including different concentrations of 3nm CdSe/ZnS and 5 nm TiO2
semiconductor quantum dots have been made by spin coating method. Their optical properties show evident
consequences of the confinement effects with wavelength bandgap shifting for both types of QDs. The confinement
effects are more pronounced for CdSe/ZnS QDs than for TiO2 QDs. Layers including CdSe/ZnS QDs exhibit a strong
luminescent behavior centred on 560nm with a stock-shift in front of the first exciton absorption peak.
The purpose of this research was to compare the optical properties and structure of tungsten oxide (WO3) thin films that
was deposited by different sputtering depositions. WO3 thin films deposited by two different depositions of direct current
(DC) magnetron sputtering and pulsed DC sputtering. A 99.95% WO3 target was used as the starting material for these
depositions. These WO3 thin films were deposited on the ITO glass, PET and silicon substrate by different ratios of
oxygen and argon. A shadow moiré interferometer would be introduced to measure the residual stress for PET substrate.
RF magnetron sputtering had the large residual stress than the other's depositions. A Raman spectrum could exhibit the
phase of oxidation of WO3 thin film by different depositions. At the ratio of oxygen and argon was about 1:1, and the
WO3 thin films had the best oxidation. However, it was important at the change of the transmittance (ΔT = Tbleached -
Tcolored) between the coloring and bleaching for the smart window. Therefore, we also found the WO3 thin films had the
large variation of transmittance between the coloring and bleaching at the gas ratios of oxygen and argon of 1:1.
Residual or internal stresses directly affect a variety of phenomena including adhesion, generation of crystalline defects,
perfection of epitaxial layers and formation of film surface growths such as hillocks and whiskers. Sputtering oxide films
with high density promote high compressive stress, and it offers researchers a reference if the value of residual stress
could be analyzed directly. Since, the study of residual stress of SiO2 and Nb2O5 thin film deposited by DC magnetron
sputtered on hard substrate (BK7) and flexible substrate (PET and PC). A finite element method (FEM) with an
equivalent-reference-temperature (ERT) technique had been proposed and used to model and evaluate the intrinsic
strains of layered structures. The research has improved the equivalent reference temperature (ERT) technique of the
simulation of intrinsic strain for oxygen film. The results have also generalized two models connecting to the lattice
volume to predict the residual stress of hard substrate and flexible substrate with error of 3% and 6%, respectively.
Normally, CdS film is used as the buffer layer in the fabrication of copper indium gallium selenide
solar cells. These solar cells can reach an efficiency of 10.3% when produced by a non-vacuum process.
However, this is a very toxic process. In this study, we propose using a nontoxic zinc sulfide (ZnS)
buffer layer which is deposited by chemical bath deposition. It took only 15 minutes to reach a ZnS
thickness of 50nm and the transmittance of the finished device was higher than 80%. The back contact
of the Mo layer sheet resistivity is 0.22 (Ω/square). The precursor solution for the cell fabrication was
prepared from anhydrous hydrazine. The film was then deposited by spraying and finally heated
rapidly to 520 without external selenization.
When a plastic substrate is under a highlight, the reflected light on the substrate always dazzles the observer. To prevent
the effect, anti-reflected (AR) coating is applied. However AR-coating is difficult to be designed with wide wavelength
range. In this research, the discontinuous metallic films were fabricated on the plastic substrates to reduce the reflection
of the plastic substrates with wide wavelength range. To reduce more reflectance, the discontinuous metallic film can
also be applied as the mask of selective ion etching to achieve rough surface. The results show the average reflectance of
the AR-coating on the plastic substrates has been decreased 5%. The average transmittance has been increased 3%.
The well-known indium-tin-oxide is not suitable for solar cell, because of the chemical reduction, even
without any hydrogen dilution. The inexpensive and non-toxic of transparent conducting Aluminum and
Gallium doped ZnO (AZO and GZO) thin films have been investigated for the substitutes for the
indium-tin-oxide thin films. AZO performs high transmittance at visible region, however, higher resistance
than GZO. In this study, AZO and GZO composed film (GAZO) will be fabricated using DC magnetron
co-sputtering deposition system to achieve lower resistance than AZO and higher transmittance than GZO.
The optical and electric properties of different thickness of GAZO such as transmittance, reflection, carrier
concentration, Hall mobility, and resistivity will be measured and analyzed.
We proposed a method to measure the optical constants of thin film through polarizing phase shifting interferometer
based on Twyman-Green interferometer structure. A broadband light source coming with a narrow band-pass filter was
used to generate a low coherence light and the wavelength is tunable by changing the filter. A pixelated micro-polarizer
mask on the detection camera made phase shifting array to make different phase shifts at once. Therefore, we can use
one single interferogram to extract phase information, and it is effective in reducing environmental vibration. The
refractive index and thickness of thin film can be derived from the obtained reflection coefficient's magnitude and phase.
The measurement results were compared with the results obtained by an ellipsometer.
A novel technique was proposed to fabricate a three-dimensional photonic crystal by self-assembling microspheres and the autocloning technology. The autocloning thin-film layers were superimposed on the prepared two-dimensional structural substrates using self-assembled microspheres. The thin-film process allows the three-dimensional periodic structure to be easily modified in the thickness dimension to structure as needed. We analyzed the etching effect using the unified process model according to the surface movement and surface velocity of the film to achieve the surface profile of the SiO2 adjusting layer. Finally, 17 layers of Ta2O5/SiO2 multilayers were stacked on the SiO2 adjusting layer successfully.
A novel design of photonic-crystal polarization filter was demonstrated with dual-band and wide working wavelength
range. The structure of the filter is a 2-dimensional wavy structure of multilayer thin films consisted with a number of
alternate high and low refractive indices transparent dielectric layers deposited sequentially on a periodic structured
substrate. The fabrication of the photonic-crystal polarization filter is based on an autocloning method which integrated
the techniques of lithography and thin film deposition. Different from the traditional polarizing beam splitters, the
photonic-crystal polarization filter is a flat type of polarizer with normal incident angle. The transmission and
reflectance spectra were analyzed using finite-difference time-domain method (FDTD). From the analysis result, we
found the photonic bandgap was happened at transverse electric (TE) mode and the passband at transverse magnetic (TM) mode. So, the photonic crystal polarization filter can separate TE mode and TM mode effectively as the field is incident normally. We design the working wavelength range of the photonic-crystal polarization filter at both visible and near infrared regions, and have wide polarization separated band at normal incident. Finally, the bandwidth is about 100 nm in visible region and 300 nm at near infrared region. The extension ratio is about 20 both in visible region and near infrared region.
Dense-wavelength-division-multiplexing (DWDM) filter is a very sensitive component in wavelength shift. The
temperature shift of central wavelength (TSCW) of filter is depended on the mechanical properties of the stress. In this
paper, a modified Stoney's equation was applied to analyze the thermal stress of DWDM filters for the reason of the
thickness ratio (thin film thickness/substrate thickness) larger than 1%. The phase-shift interferometer and TSCW were
applied to measure and achieve the coefficient of thermal expansion (CTE), biaxial modulus, temperature optical
coefficient, stress optical coefficient, and Poisson ratio of DWDM filter. Based on this method, we can obtain the CTE of
DWDM filter 0.87pm/ °C ,the biaxial modulus 41 GPa, Poisson ratio 0.22, temperature optical coefficient 1.4×10-5 / °C, and stress optical coefficients -1.9×10-12 /Pa. To achieve zero TSCW for a DWDM filter, the CTE of the substrate should be 10.36ppm/ °C.
Hydrogenated microcrystalline silicon (μc-Si:H ) thin films have attracted many attentions due to the high mobility
compared with the amorphous silicon (a-Si) thin films. To fabricate μc-Si:H thin films, plasma-enhance chemical vapor
deposition (PECVD) is the most popular method. The disadvantages of PECVD are the high facility cost and using the
toxic processing gases such as silane (SiH4). Whereas there is no these disadvantages using radio-frequency (RF)
magnetron sputtering to deposit silicon thin films. Unfortunately, the silicon thin films deposited by the regular RF
magnetron sputtering are a-Si. In this study, μc-Si:H thin films were fabricated using RF magnetron sputtering with
argon and hydrogen as working gas at low substrate temperature (Ts=250°C and 350°C).The grain sizes, crystal volume
fractions and photosensitivity (ratios of dark conductivities and photo conductivities) of the μc-Si:H thin films which
deposited with different hydrogen partial pressures and sputtering powers were analyzed. The results showed that the
grain sizes and the crystal volume fractions were increased and the photosensitivity was decreased as the hydrogen
partial pressure increased at the sputtering power 200W. The grain size was between 15 to 20 nm and the crystal volume
fractions was between 75 to 80% when the hydrogen partial pressure was over 90%.
The triangle shape of two dimensional photonic crystals were fabricated based on autocloning technique, and preserved
the periodic surface corrugation after the deposition of multilayer stacks using an E-beam gun evaporation with ion-assisted
deposition (IAD). Drude model has been applied to analyze the effective refractive indices of the structural
single-layer and multilayer autocloning films with triangle shape in the visible range which divided into several periodic
parts. The advantage of using the model of effective refractive index is the optical properties of structural multilayer
films can be analyzed easily. The effective refractive indices have been calculated based on this model, and simulated
the reflectance and transmittance of the different incident angles. The influences of the structure period on the
reflectance and transmittance were also analyzed.
Autocloning technique is an attractive deposition method to make photonic crystals since it can produce various photonic crystals by changing the substrate periodicity and the structure of the stacking materials. We report a novel method to fabricate autocloned photonic crystals. This method has better step-coverage, higher deposition rate and large deposition area than the sputtering method. We successfully preserved the periodic surface corrugation after the deposition of multilayer stacks by using an E-beam gun evaporation with ion-assisted deposition (IAD). Freedoms of the shaping process can be controlled by the power of IAD and the time of the ion source etching. The ion source etching is a physical etching process without any chemical reaction and dangerously reactive gas. The process parameters were described in this paper. During the deposition process, the refractive index can be adjusted by changing the deposition rate and the substrate temperature. The deposition rate was about 0.7~1 nm/s for SiO2 which is almost ten times faster than the sputtering method. So this method is good for the mass production of photonic crystals.
Dense Wavelength Division Multiplexers (DWDM), a kind of narrow band-pass filter, are extremely sensitive to the optical thickness error in each composite layer. Therefore to have a large useful coating area is extreme difficult because of the uniformity problem. To enlarge the useful coating area it is necessary to improve their design and their fabrication. In this study, we discuss how the tooling factors at different positions and for different materials are related to the optical performance of the design. 100GHz DWDM filters were fabricated by E-gun evaporation with ion-assisted deposition (IAD). To improve the coating uniformity, an analysis technique called shaping tooling factor (STF) was used to analyze the deviation of the optical thickness in different materials so as to enlarge the useful coating area. Also a technique of etching the deposited layers with oxygen ions was introduced. When the above techniques were applied in the fabrication of 100 GHz DWDM filters, the uniformity was better than +/-0.002% over an area of 72 mm in diameter and better than +/-0.0006% over 20mm in diameter.
When sampling a periodic image that includes high spatial frequencies with a digital image device, alias distortion is
always produced. To reduce the distortion, an optical low-pass spatial filter (OLPF), which cuts off the high spatial
frequency, can be applied. In this study thin-film phase grating optical low-pass filter (GOLF) with two-phase and three-phase
of have been analyzed. By matching the period of the grating to the thickness of the thin film of two-phase GOLF,
the cut-off bandwidth was twice of the pass bandwidth. By using the same technique, the cut-off bandwidth of three-phase
GOLF was five times of the pass bandwidth. Two-phase GOLF was fabricated by using physical vapor deposition
technology with a metal mesh as mask and showed advantages of being simple, cheap and good for mass-production as
compared with the conventional methods. The surface profiles of the thin-film phase GOLF was measured by a white
light interferometer. The optical property, the modulation transfer function (MTF) was measured by a MTF
measurement system. Both results showed good agreement with the theoretical calculation. The image of a digital image
device also showed the Moire pattern was suppressed successfully by the thin-film phase GOLF.
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