About sixty years ago, the biological cell counter with an electrical currents detection technique through a micrometer size orifice was invented by Dr. Coulter. A couple of years ago, the ultrafast portable pore device (MinION) with an electrical detection technique was manufactured by Oxford Nanopore Technology. However, high error rates over 80% from this solid state nanopore device is initially reported in several journals. The high error rates may have been contributed from the electrical double layer formed in the pore channel. Even though the error rates have been reduced significantly. Considering the fact that most biosensors are utilizing the optical detection technique, the optical pore device can be an excellent candidate for the next generation single molecule sensor. We will report the fabrication process of the plasmonic optical nanopores.
The Au nano-hole surrounded by the periodic nano-patterns would provide the enhanced optical intensity. Hence, the nano-hole surrounded with periodic groove patterns can be utilized as single molecule nanobio optical sensor device. In this report, the nano-hole on the electron beam induced membrane surrounded by periodic groove patterns were fabricated by focused ion beam technique (FIB), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Initially, the Au films with three different thickness of 40 nm, 60 nm, and 200 nm were deposited on the SiN film by using an electron beam sputter-deposition technique, followed by removal of the supporting SiN film. The nanopore was formed on the electron beam induced membrane under the FESEM electron beam irradiation. Nanopore formation inside the Au aperture was controlled down to a few nanometer, by electron beam irradiations. The optical intensities from the biomolecules on the surfaces including Au coated pyramid with periodic groove patterns were investigated via surface enhanced Raman spectroscopy (SERS). The fabricated nanopore surrounded by periodic patterns can be utilized as a next generation single molecule bio optical sensor.
Recently the single molecules such as protein and deoxyribonucleic acid (DNA) have been successfully characterized by using a portable solidstate nanopore (MinION) with an electrical detection technique. However, there have been several reports about the high error rates of the fabricated nanopore device, possibly due to an electrical double layer formed inside the pore channel. The current DNA sequencing technology utilized is based on the optical detection method. In order to utilize the current optical detection technique, we will present the formation of the Au nano-pore with Au particle under the various electron beam irradiations. In order to provide the diffusion of Au atoms, a 2 keV electron beam irradiation has been performed During electron beam irradiations by using field emission scanning electron microscopy (FESEM), Au and C atoms would diffuse together and form the binary mixture membrane. Initially, the Au atoms diffused in the membrane are smaller than 1 nm, below the detection limit of the transmission electron microscopy (TEM), so that we are unable to observe the Au atoms in the formed membrane. However, after several months later, the Au atoms became larger and larger with expense of the smaller particles: Ostwald ripening. Furthermore, we also observe the Au crystalline lattice structure on the binary Au-C membrane. The formed Au crystalline lattice structures were constantly changing during electron beam imaging process due to Spinodal decomposition; the unstable thermodynamic system of Au-C binary membrane. The fabricated Au nanopore with an Au nanoparticle can be utilized as a single molecule nanobio sensor.
Metallic nanoantennas are able to spatially localize far-field electromagnetic waves on a few nanometer length scale in the form of surface plasmon excitations 1-3. Standard tools for fabricating bowtie and rod antennas with sub-20 nm feature sizes are Electron Beam Lithography or Ga-based Focused Ion Beam (FIB) Milling. These structures, however, often suffer from surface roughness and hence show only a limited optical polarization contrast and therefore a limited electric field localization. Here, we combine Ga- and He-ion based milling (HIM) for the fabrication of gold bowtie and rod antennas with gap sizes of less than 6 nm combined with a high aspect ratio. Using polarization-sensitive Third-Harmonic (TH) spectroscopy, we compare the nonlinear optical properties of single HIM-antennas with sub-6-nm gaps with those produced by standard Ga-based FIB. We find a pronounced enhancement of the total TH intensity of more than three in comparison to Ga-FIB antennas and a highly improved polarization contrast of the TH intensity of 250:1 for Heion produced antennas 4. These findings combined with Finite-Element Method calculations demonstrate a field enhancement of up to one hundred in the few-nanometer gap of the antenna. This makes He-ion beam milling a highly attractive and promising new tool for the fabrication of plasmonic nanoantennas with few-nanometer feature sizes.
Recently the single molecules such as protein and deoxyribonucleic acid (DNA) have been successfully characterized using a solidstate nanopore with an electrical detection technique. However, the optical plasmonic nanopore has yet to be fabricated. The optical detection technique can be better utilized as next generation ultrafast geneome sequencing devices due to the possible utilization of the current optical technique for genome sequencing. In this report, we have investigated the Au nanopore formation under the electron beam irradiation on an Au aperture. The circular-type nanoopening with ~ 5 nm diameter on the diffused membrane is fabricated by using 2 keV electron beam irradiation by using field emission scanning electron microscopy (FESEM). We found the Au cluster on the periphery of the drilled aperture under a 2 keV electron beam irradiation. Immediately right after electron beam irradiation, no Au cluster and no Au crystal lattice structure on the diffused plane are observed. However, after the sample was kept for ~ 6 months under a room environment, the Au clusters are found on the diffused membrane and the Au crystal lattice structures on the diffused membrane are also found using high resolution transmission electron microscopy. These phenomena can be attributed to Ostwald ripening. In addition, the Au nano-hole on the 40 nm thick Au membrane was also drilled by using 200 keV scanning transmission electron microscopy.
KEYWORDS: Gold, Electron beams, Transmission electron microscopy, Carbon, Particles, Chemical species, Contamination, Fabrication, Scanning electron microscopy, Statistical analysis
There have been tremendous interests about the fabrication of the Au plasmonic nanopore due to its capability of the nanosize optical biosensor. We have investigated the influence of low energy electron beam irradiation on an Au nanomembrane during Au nanopore formation. In this report, the influence of electron beam irradiation on the Au nanopore formation will be reported. The nanopores on the 200 nm thick Au membrane were initially fabricated using focused ion beam (FIB) and high energy electron beam techniques such as transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). During high energy electron beam by using TEM, either a "shrinking" or a "opening" phenomenon is reported dependent on the ratio of thickness to aperture diameter. However, for a FESEM electron beam irradiation, a shrinking phenomenon is always observed. In this report, the nanopore formation during FESEM electron beam irradiation will be reported depending upon energy absorption and thermal diffusivity.
KEYWORDS: Electron beams, Gold, Transmission electron microscopy, Absorption, Biosensors, Scanning electron microscopy, Silica, Molecules, Plasmonics, Ion beams
There have been tremendous interests about the fabrication of the Au plasmonic nanopore due to its capability of the nanosize optical biosensor. We have investigated the influence of low energy electron beam irradiation on an Au nanomembrane during Au nanopore formation. In this report, the influence of electron beam irradiation on the Au nanopore formation will be reported. The nanopores on the 200 nm thick Au membrane were initially fabricated using focused ion beam (FIB) and high energy electron beam techniques such as transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). During high energy electron beam by using TEM, either a “shrinking” or a “opening” phenomenon is reported dependent on the ratio of thickness to aperture diameter. However, for a FESEM electron beam irradiation, a shrinking phenomenon is always observed. In this report, the nanopore formation during FESEM electron beam irradiation will be reported depending upon energy absorption and thermal diffusivity.
KEYWORDS: Electron beams, Gold, Transmission electron microscopy, Silicon, Chemical species, Scanning electron microscopy, Nanolithography, Liquids, Microfabrication, Metals
Recently there have been tremendous interests about the fabrication of the solid state nanopore due to its capability of the nanosize biosensor. In this report, the dynamics of the Au nanopore formation on the pyramidal membrane will be reported. The nanopores on the microfabricated Au coated SiO2 pyramid were fabricated using focused ion beam (FIB) and high energy electron beam techniques such as transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). For high scanning electron beam irradiation using FESEM, shrinking of the Au nanopore was always observed. The nanopore formation dependent upon the primary electron voltage, and the scan rate of the FESEM electron beam was carefully examined. The higher closing rates for the faster scan rate and the lower electron accelerating voltage are observed. For the TEM electron beam exposure, the closing or the opening of the pore was observed depending upon the electron beam current. We do believe that this phenomenon can be attributed to the capillary force and the vaporization of the materials on the viscous liquid membrane due to TEM electron beam irradiation.
The Al Nano apertures surrounded by periodic patterns on the pyramidal structures were fabricated. The nanometric size aperture with ~ 100 nm diameter surrounded by equidistant elliptic groove patterns presented greater transmission than the aperture with circular groove patterns. The translocation of λ-DNA through these fabricated nanostructures was tested using electrically biased techniques. We observed the strong fluorescent optical signal from the translocated DNA through the nanoprobe with a charge coupled device camera. The optical force driven DNA translocation though a nanoprobe surrounded with elliptically patterned grooves is under investigation.
Recently there has been tremendous interest about the dynamical sequence of fabrication of the solid state nanopore due to its capability of the nanosize solid state biosensor as a single molecule sensor. Depending upon the instruments such as transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM), the dynamics of nanopore formation present different physical mechanisms. In this report, formation of the nanopores was examined. Metallic nanopores with ~ 50 nm diameter on top of the oxide pyramid were fabricated using conventional Si microfabrication techniques followed by wet isotropic etching of the oxide; sputter metal deposition followed by the focused ion beam (FIB) techniques. No shrinking phenomena were observed for the nanopore diameter greater than 50 nm under electron beam irradiation using TEM. However, for high scanning electron beam irradiation using FESEM, shrinking of the Au nanopore was always observed. We do believe that these phenomena can be attributed to the liquid phase surface modification for TEM electron beam and adiabatic solid state phase surface modification for high scanning FESEM. For a huge amount of energy input from high scan rate and the poor thermal conduction to its surrounding area, the energy spike inside the electron penetration area would occur. However, a TEM electron beam irradiation without repetitive scan can provide the liquid phase surface modification.
Recently there have been tremendous interests about the fabrication of the solid state nanopore due to the capability of
the solid state nanopore as a single molecule sensor. The SiN nanopore and the SiO2 nanopore have been fabricated with
high energy electron beam exposure such as transmission electron microscopy, field emission electron microscopy, and
focused ion beam sculpting. However, the plasmonic Au nano-pore can be utilized as a nanobio optical sensor due to the
106 fold increase of the Raman signal intensity. Hence, in this report, the fabrication of the plasmonic nanopore with less
than ~ 10 nm on the apex of the micronsize pyramidal structure using various high energy electron beam exposure.
Under the electron beam exposure of FESEM followed by EPMA, the widening and the shrinking of the Au nanopore
were observed depending upon the EPMA probe current. The diameters of the Au nanopore was also reduced
successively from ~ 5 nm down to zero using 200 keV TEM. From these experimental results, the dynamics of the
nanopore formation are found to depend on the viscosity of the membrane, radiation damage, and evaporation of the
materials under high vacuum condition. This fabricated plasmonic nano-pore device can be utilized as geneome
sequencing device or a single-molecule sensor.
Recently there have been tremendous interests about the single molecule translocation through the SiN nanopore array.
For DNA translocation and characterization, SiN nanopore array is easy to fabricate with high energy electron beam
exposure. It is well known that the metallic nanopore can provide the huge enhancement, 106 fold increase of the
electromagnetic field at the metallic nanopore due to "hot spot" effect. In addition, the fabricated plasmonic micro device
provides huge photon transmission through the fabricated nanochannel. In this report, we microfabricated the plasmonic
nanopore with ~ 101 nm on top of the micronsize pyramidal structure for translocation and optical characterization using
conventional microfabrication process and electron beam heating. The reduced Au nanopore due to electron beam
heating is found to provide the huge optical transmission resulted in the huge photonic pressure gradient between the free
space and nanopore inside. The huge pressure gradient can be attributed to the resonance transmission between the
fabricated V groove cavity and the nanosize waveguide formed during the metal deposition. This fabricated plasmonic
nano-aperture device can be utilized as bio-molecule translocation and optical characterization.
We microfabricated the plasmonic nanopore with ~ 1 nm on top of the pyramid for single molecule dynamics. This
plasmonic micro device provides huge photon transmission through the fabricated nanochannel on the top of the
pyramidal structure. This can generate the huge photonic pressure gradient between the free space and nanopore inside.
The huge pressure gradient can be attributed to the resonance transmission between the fabricated V groove cavity and
the nanosize waveguide formed during the metal deposition. This fabricated huge photonic device can be utilized as biomolecule
translocation and single molecule dynamics.
Electric field enhancement has been actively studied recently and many metallic structures that are
capable of locally enhancing electric field have been reported. The Babinet's principle can be utilized,
especially in the form of Booker's extension, to transform the known electric field enhancing structures
into magnetic field enhancing structures. The authors explain this transformation process and discuss
the regime in which this principle breaks down. Unless the metals used can be well approximated with
a PEC model, the principle's predictions fails to hold true. Authors confirm this aspect using numerical
simulations based on realistic material parameters for actual metals. There is large discrepancy
especially when the structural dimensions are comparable or less than the skin-depth at the wavelength
of interest. An alternative way to achieve magnetic field enhancement is presented and the design of a
connected bow-tie structure is proposed as an example. FDTD simulation results confirm the operation
of the proposed structure.
e macro size pyramidal horn probe such as klystron horn antenna has been used to provide the excellent focusing
capabilities in microwave region. In the similar way, the pyramidal probe with the micron size mirror (pyramidal horn
probe) has been fabricated with a nano-size aperture with diameter ranging from 30 to 330 nm on its apex. Light
transmission through the micro-fabricated pyramidal horn probe has been measured to enhance the light transmission
due to resonant effects between the cavity mode and the slit modes in the probe, along with directionality of the
transmitted beam. The resonant tunneling between two standing waves in the input groove and in the output groove can
provide the transmission enhancements. Below ~170 nm, the output power normalized to the input power (ratio) has
been increased with decreasing diameter. On the other hand, for the diameter ranging from 330 to 170 nm, the ratio has
been decreased with decreasing diameter. The transmission (T) is measured to be inversely proportional to the area (A),
and TA value for input wavelength 532 nm is found to be constant, 0.136 for the diameter below 160 nm, and to be
0.053 for diameter greater than 160 nm.
KEYWORDS: Signal processing, Logic, Logic devices, Binary data, Optical circuits, Optical components, Signal attenuation, Data conversion, Digital electronics, Eye
All-optical 4-bit Gray code to binary coded decimal (BCD) converter was demonstrated, for the first time in our
knowledge, with the number of 12 SOAs by means of commercially available numerical analysis tool (VPI). Circuit
design approach was modified appropriately in order to fit the electrical method on an all-optical logic circuit based on
cross gain modulation (XGM) process so that signal degradation due to the non-ideal optical logic gates can be
minimized. In our approach, only using XGM process as a nonlinear function, the maximum number of XGM process
serially underwent by input signals is twice at the most insuring signal quality. Without regenerations, Q-factor of around
4 was obtained for the most severely degraded output bit (least significant bit - LSB) with 2.5Gbps clean input signals
having 20dB extinction ratio. It is worth to note that, implementing this LSB is complex enough to give it as an example
of a 4-bit conversion system. While modifying two-level simplification method and Karnaugh map method to design
Gray code to BCD converter, general design concept was also founded in this research not only for the Gray code to
BCD converter but also for any general applications such as encoder / decoder, multiplexer / demultiplexer, and read
only memory so that readers can develop their own all-optical logic device easily using XGM process in SOAs.
In this paper, we will briefly outline our contributions for the physical realization of coded OTDR, along with its
principles and also highlight recent key results related with its applications. For the communication network application,
we report a multi-port / multi-wavelength, high-speed supervisory system for the in-service monitoring of a bidirectional
WDM-PON system transmission line up to 16 ports x 32 nodes (512 users) capacity. Monitoring of individual branch
traces up to 60 km was achieved with the application of a 127-bit simplex code, corresponding to a 7.5dB SNR coding
gain effectively reducing the measurement time about 30 times when compared to conventional average mode OTDR.
Transmission experiments showed negligible penalty from the monitoring system to the transmission signal quality, at a
2.5Gbps / 125Mbps (down / up stream) data rate. As an application to sensor network, a Raman scattering based coded-OTDR distributed temperature sensor system will be presented. Utilizing a 255-bit Simplex coded OTDR together with
optimized sensing link (composed of cascaded fibers with different Raman coefficients), significant enhancement in the
interrogation distance (19.5km from coding gain, and 9.6km from link-combination optimization) was achieved to result
a total sensing range of 37km (at 17m/3K spatial/temperature resolution), employing a conventional off-shelf low power
(80mW) laser diode.
In this paper, we provide a detailed performance analysis of an nc-Si EDWA for the real application. Optical gain (small signal / saturation regime), noise figure and required pump density has been assessed in terms of the device structure. Results show a high feasibility of achieving 10dBm output power with 0dBm of input signal, using an array of commercially available high-power blue-green LEDs as the top pump. In numerical model section, we suggest simplified coupled rate equation and 2-D propagation equation constructed to investigate amplifier performance. In performance analysis section, firstly, we compared population inversion characteristics for Er with/without nc-Si condition to confirm the widening of high inversion region by introducing nc-Si sensitizer, which means less pump intensity requirement for same input signal power. In addition, to test the feasibility of the NC-EDWA for the metro-network applications, we simulated the amplifier performance for varying the width of amplifier region. With 50x7μm2 active core and bottom mirror, only 15.8 W/cm2 (8.8 W/cm2 for 100μm width) of pump intensity was sufficient to meet the target operating condition. We also compare the inversion distributions of NC-Si EDWA, for the 4 types of EDWA structures under investigation (straight without/with mirror, adiabatic without/with mirror). As another key performance factor, we also calculated noise figures for different NC-Si EDWA structures.
We present system-level characterization results of a MEMS tunable optical filter with a flat-top passband and narrow transition bands. The proposed optical bandpass filter can continuously change its optical bandwidth and center wavelength using a free-space grating and a variable-aperture MEMS reflector. We observed that the receiver sensitivity degradation is within 1 dB across the 6-dB optical passband.
KEYWORDS: Raman spectroscopy, Single mode fibers, Optical amplifiers, Phase shifts, Complex systems, Signal attenuation, Interference (communication), Optical filters, Fiber amplifiers, Signal to noise ratio
We present an efficient algorithm for the search of optimum design parameters and transmission quality factor (Q) for a Raman amplified transmission system. By treating the nonlinear phase shift (NPS) as the key parameter for the determination of secondary system parameters, and then scanning the nonlinear Schrödinger equation (NLSE) to get the optimum Q factor as a function of NPS only, we show that the multi-dimensional, multi-parameter, time-consuming design process can be reduced to a highly efficient semi-analytic, 1 dimensional numerical optimization problem. As an application example for the suggested algorithm, we determine the optimum system design parameters (input powers to SMF, DCF, distributed Raman gain, and forward Raman pumping ratio) and Q factor for a single channel 10 G bit/s 2000 km transmission link (SMF-DCF), and then study the effect of pump-relative-intensity-noise (RIN) and span length change to the optimum Q values and changes in the optimum design point. Results show a Q factor improvement for the system more than 1.16dB / 4.89dB at 100km / 200km span length with our design method, when compared to previous optimization method.
KEYWORDS: Raman spectroscopy, Optical amplifiers, Fiber amplifiers, Single mode fibers, Signal processing, Signal attenuation, Picosecond phenomena, Signal to noise ratio, Nonlinear optics, Phase shifts
Transmission systems employing Raman amplifier technology have to put up with much higher level of design complexities, when compared to conventional transmission lines with doped fiber optical amplifier. Even for the construction of a fundamental, basic building block - a unit of a fiber Raman amplifier (FRA), the designer have to struggle with the problems associated with the interactions between pump / signal waves mediated by Raman process, have to wander within the vast degrees of freedom given the choice of pumping directions / ratios, and have to contemplate with the wavelength dependent fiber loss / noise figure profiles. The problem further evolves into steps-higher, demanding and time-consuming one when extended to that of a system design employing Raman amplifiers. Optimizing OSNR and designing ultra-long haul links with best Q performances, while adjusting variables in the span length, Rayleigh penalty, pump noise, nonlinear penalty, dispersion and gain distribution is a problem which can be easily stated, but in reality is not a process which can be easily achieved. We present efficient, optimal design methods for Raman amplified WDM transmission links: 1. for the multi-channel gain flatness, 2. transient control under signal reconfigurations, and 3. for the estimation of optimum system Q value and corresponding link design parameters.
Increasing demands on the high capacity wavelength division multiplexed (WDM) transmission system now require newly developed transmission windows beyond the gain bandwidth supported by erbium-doped fiber amplifiers (EDFA). With the intensive development efforts on new rare-earth dopants and fiber nonlinearity (Raman process) for fast few years, wideband optical amplifiers now can support easily over 4-5 fold wider gain bandwidth than it was formerly possible with the conventional EDFAs. Of various breeds for this application, there exist three distinct approaches near 150nm band, accessible in the commercial market. These include: Thulium-doped fluoride fiber amplifiers (TDFA) for S+band (1450-1480 nm) and S band (1480-1530 nm), EDFAs for C band (1530-1560nm) and L band (1570-1610nm) and L band (1570-1610nm), Raman amplifiers with 100 nm's of gain bandwidth (with flexible location from S+ to L Band), and hybrid amplifiers with serial/parallel combinations of above techniques. Even though there have been much increased experimental reports for all of these amplifiers, the complexity of the amplification dynamics from the number of involving energy levels and difficulty in measuring experimental parameters make it harder than ever to predict the performance of wideband amplifiers in general. This lack of serious study on the analytic or numerical analysis on wideband amplifiers could cause the future impairments for the prediction and estimation of the amplifier performances for different applications, restricting the successful deployment of wideband amplifier based transmission systems. In this paper, we present the numerical model and analysis techniques for wideband amplifiers (C/L band EDFA, Raman amplifier, and TDFA),along with their application examples.
Nondegenerate four-wave mixing in semiconductor optical amplifiers was studied both as a spectroscopic tool for probing semiconductor dynamics and as a wavelength conversion technique. Four-wave mixing spectra were measured at detuning frequencies ranging from GHz to THz rates and ultrasfast intraband mechanisms having relaxation time constants of 650 fs and less than 100 fs were revealed in the measurements. Cross-polarization four-wave mixing was also measured to study the inter quantum-well carrier transport process in quantum-well amplifiers. In addition, broadband wavelength conversion using four-wave mixing in semiconductor optical amplifiers was investigated. Results concerning the conversion efficiency over spans up to 65 nm, as well as a demonstration of wavelength conversion with gain are presented. The issue of converted signal-to-background noise in this process is also addressed.
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