A plasmonic integrated circuit configuration comprising plasmonic and electronic components is presented and the feasibility for high-speed signal processing applications is discussed. In integrated circuits, plasmonic signals transmit data at high transfer rates with light velocity. Plasmonic and electronic components such as wavelength-divisionmultiplexing (WDM) networks comprising metal wires, plasmonic multiplexers/demultiplexers, and crossing metal wires are connected via plasmonic waveguides on the nanometer or micrometer scales. To merge plasmonic and electronic components, several types of plasmonic components were developed. To ensure that the plasmonic components could be easily fabricated and monolithically integrated onto a silicon substrate using silicon complementary metal-oxide-semiconductor (CMOS)-compatible processes, the components were fabricated on a Si substrate and made from silicon, silicon oxides, and metal; no other materials were used in the fabrication. The plasmonic components operated in the 1300- and 1550-nm-wavelength bands, which are typically employed in optical fiber communication systems. The plasmonic logic circuits were formed by patterning a silicon oxide film on a metal film, and the operation as a half adder was confirmed. The computed plasmonic signals can propagate through the plasmonic WDM networks and be connected to electronic integrated circuits at high data-transfer rates.
We have developed near-infrared imaging equipment that can detect small organic substances in foodstuffs with thicknesses of more than 1 mm. The equipment is composed of a high output laser diode and a CMOS camera. The irradiated light power distribution was highly uniform with a maximum optical density of 1.3 W/cm2. A 0.3-mmdiameter wooden stick covered with a 2-mm-thick layer of ham can easily be distinguished in the images. The bones in fish and in chicken wing sticks could also be distinguished. The thicknesses of the fish and the chicken wing sticks were approximately 30 mm and 20 mm, respectively. We eliminated the low spatial frequency components from the images to improve the image contrast.
A surface plasmon polariton (SPP) is composed of collective electron oscillations that confine optical energies in nanoscale
beyond the diffraction limit. This advantage of SPPs has promoted the development of high-density optoelectronic
integrated circuits (OEICs) using SPPs. Schottky-type plasmonic detectors have attracted particular attention, because
these devices show sensitivity in the telecommunications wavelength range and can be integrated into Si-based
electronic circuits with a simple fabrication process. We have developed an Au/Si Schottky-type plasmonic detector with
nano slits that excites SPPs at the Au/Si interface. In this report, we demonstrate a novel nano-slit arrangement that
provides a sensitivity improvement for the detector. Using the finite-difference time-domain method, we have shown that
the highest electric field intensity in the SPP mode on the Au/Si interface is generated by positioning slits with twice the
pitch of the SPP wavelength at the Au/Si interface. Using this slit pitch, a weaker SPP mode intensity on the air/Au
interface and a stronger SPP mode intensity at the Au/Si interface have also been confirmed. Nano slits with different slit
pitches were formed in the Au film of the detector, and the slit pitch dependence of the photocurrent was measured. The
experimental results showed similar tendencies to the simulation results. This novel nano-slit arrangement can provide an
efficient plasmonic detector for future high-speed data processing applications.
The operation of a metal-oxide-semiconductor field-effect transistor (MOSFET) by a surface plasmon (SP) signal was
demonstrated. The SP detector, composed of a gold/silicon Schottky diode with a nano-slit grating, was monolithically
integrated with the MOSFETs on a silicon substrate. SP generation by the nano-slit gating (slit width of 100 nm, slit
pitch of 440 nm, and slit depth of 300 nm) was confirmed by analytical calculations based on the finite-difference timedomain
method. The SP detector operated at a photon energy (0.80 eV) that was below the bandgap energy of silicon
(1.1 eV), with responsivity of 24 nA/mW and a dark current of 1.7 nA under reverse bias of 5.0 V. The photocurrent
generated by the SP detector controlled the drain current of a monolithically integrated MOSFET.
Contamination of foodstuffs with foreign substances is a serious problem because it often has negative effects on
consumer health. However, detection of small organic substances in foods can be difficult because they are undetectable
with traditional inspection apparatus. In this work, we developed new equipment that can detect small organic
contaminant substances in food at high speed using a near-infrared (NIR) imaging technique. The absorption spectra of
various foods were measured, and the spectra showed low absorbance at wavelengths from 600 nm to 1150 nm. Based
on the observable wavelength range of a CMOS camera, which has a high dynamic range, superluminescent diodes
(SLDs) with a wavelength of 830 nm were selected as light sources. We arranged 40 SLDs on a flat panel and placed a
diffusion panel over them. As a result, uniformly distributed light with an intensity of 0.26 mW/cm2 illuminated an area
of 6.0 cm × 6.0 cm. Insects (3 mm wide) and hairs (0.1 mm in diameter) were embedded in stacked ham slices and in
chocolate, with a total thickness of 5 mm in each case, and the transmission images were observed. Both insects and
hairs were clearly observed as dark shadows with high contrast. We also compensated the images by using software
developed in this study to eliminate low spatial frequency components in the images and improve the sharpness and
contrast. As a result, the foreign substances were more clearly distinguished in the 5-mm-thick ham.
Grating inscription in azo-dye doped polymers is an interesting phenomenon because of its high diffraction performance and applicability to real-time 3D displays. Although some of these materials were investigated under no external electric field with symmetric optical alignments in preceding studies, they often showed a phase shift of periodic modulation of refractive index from the interference fringe formed by irradiation beams, resulting in asymmetric energy exchange between two coupled beams. The mechanism of the behavior has been usually attributed to the molecular motions triggered by trans-cis isomerization, but their details are still unknown. Therefore, studies on temporal evolution of the process and their translation into physical meaning are necessary. In order to investigate the evolution of grating inscription and phase shift, several methods have been developed. In this study, we analyzed the coupled wave equations proposed by Kogelnik, and derived general solution applicable to the system with both phase and amplitude gratings with arbitrary phase relationship. We showed that the analysis based on the equation can give a direct evidence of the phase shift between the phase and amplitude gratings if it exists. This method was applied to the fringe pattern inscribed in thick films of PMMA doped with an azo-carbazole dye, showing that observed signals indicated the phase deviation between two types of gratings.
Optical circuits are needed to achieve high-speed, high-capacity information processing. An optical waveguide is an essential element in optical circuits. Electrospun polymer fibers have diameters in the nanometer range and high aspect ratios, so they are prime candidates for small waveguides. In this work, we fabricate uniform electrospun polymer nanofibers and characterize their optical waveguiding properties. Poly(methyl methacrylate) (PMMA) solutions of different concentration that contain a small amount of Nile Blue A perchlorate (NBA) are electrospun. Uniform PMMA/NBA nanofibers are obtained from the 10 wt% solution. The fibers are covered with transparent cladding and their ends cut vertically. A laser beam with a wavelength of 533 nm is irradiated onto the fiber from the direction vertical to the fiber axis so that it scans along the fiber. Photoluminescence (PL) at the end face of individual fibers is then measured. The PL intensity decreases with increasing distance (d) between the end face of a fiber and irradiating point of the laser beam as ~exp(-αd) with a loss coefficient (α). Measurements of five individual fibers reveal α is in the range of 17–75 cm-1.
Real-time imaging techniques are required in diverse fields, such as food factory production lines for food quality
monitoring, and in the medical profession for clinical diagnosis. For these purposes, magnetic resonance imaging and X-ray
computed tomography have been developed; however, these techniques are difficult to use and expensive, and cannot
detect organic, wooden, or plastic foreign objects in food. Optical measurement methods, in contrast, are simple and
cheap, and are suitable for real-time monitoring. Optical coherence tomography and photo-acoustic tomography
techniques have been developed, but are not classified as real-time imaging techniques as a certain time interval is
necessary for computation and imaging. For real-time light-based imaging, we previously developed a compact system
using near infrared light, which could detect insects and human hair in food and the blood vessels in the human body. In
this study, we describe an improved system in which organic foreign objects or substances in food and bones in chicken
wings can be imaged in real time using diffused light. The system consists of an optical source, composed of
superluminescent diodes emitting 830-nm light, a certain optical system eliminating scattering light, and a CMOS sensor
covering a wide dynamic range. Foreign substances, such as human hairs and insects, are clearly detected in images of 5
mm-thick chocolate. The bone structures in 20 mm-thick chicken wings are also imaged in real-time.
A compact optical correlator that can retrieve shape, color, and texture information was improved and optimized for
medical applications. Some optical components of the optical correlator were changed to eliminate stray light. Tumor
and normal cell images from rats can be clearly distinguished by using their color and luminance information. Here, the
color and luminance data from the cell images were converted into two-dimensional patterns on the x-y chromaticity
diagram and the luminance histogram, respectively. The tumor cell images were clearly distinguished from large
numbers of cells by retrieving the color and luminance patterns. Based on these results, we have demonstrated that our
optical correlator is an effective tool for retrieval of complicated large volume information, such as that of cell images.
In this study, we present an analysis of optical frequency signal transmission through the whispering gallery mode
(WGM) generated in a silica microsphere for the application of optical frequency signal transmission to integrated
circuits. The behavior of the WGM within a microsphere was analyzed in detail using the finite-difference time-domain
method. The electric field distribution in the silica microsphere led to the WGM, and the electric field was amplified
within the microsphere. The interval between the peaks of the WGM (free spectral range of the microcavity) was clearly
observed in the wavelength spectrum. When two light beams having slightly different wavelengths were guided into the
microsphere, a beat frequency corresponding to the difference frequency of the two light beams was also obtained in the
simulation. The simulation results were experimentally confirmed by observing the WGM and the beat signal generated
in a silica microsphere. From these results, we have theoretically and experimentally clarified the feasibility of optical
frequency signal transmission through the WGM.
We present a technique for monitoring alien substances in foods and blood vessels in the human body. A prototype of the
system using near-infrared rays is developed, and its applicability to food is analyzed in detail. The system developed is
basically composed of an optical source and a CMOS sensor. Some optical components adjusted at 850-nm band are also
set in the system. The system can monitor organic alien substances intentionally added to foods and blood vessels. The
clarity of the image increased with decreasing water content and homogeneous material density. The resolving power of
the images was confirmed to be about 100 μm. This technique will be useful for our safety and health in our daily lives.
A compact optical correlator applicable to the retrieval of colour and texture as well as shape information was developed.
A new technique for retrieving colour and texture information by using a slot-in-type compact joint-transform correlator
(JTC) with minimum size (140 (W) × 220 (L) × 40 mm (H)) was developed. The developed techniques were used to
retrieve images of fruits and vegetables, taken by the digital camera. The developed technique can retrieve images of
certain fruits, such as an apple, from images of many different fruits and vegetables. It will open up a new area of
retrieval techniques for ambiguous images based on shape, colour and texture information.
A plasmonic Raman sensor using periodic hole arrays was investigated numerically and experimentally. In previous
work, we fabricated a hole array in a thin metal film on a dielectric substrate using focused ion beam lithography and
succeeded in observing surface plasmon resonance. Those experimental results agreed well with simulation results (for
an array of cylindrical holes) obtained using the finite-difference time-domain method. However, a cylindrical hole array
provides insufficient sensitivity (i.e., electric field enhancement) for measuring surface-enhanced Raman scattering
(SERS). Therefore, we enhanced the electric field by using focusing holes (tapered structure), which we expected to
would give us a larger electric field than the cylindrical holes. Furthermore, for a hole array, we optimized the structural
design in terms of metal film thickness, hole diameter, and hole period on the basis of theoretical predictions. We
successfully designed and fabricated an arbitrary localized surface plasmon resonance for the optimized array for the
excitation wavelength (λ= 632.8 nm) for the target molecule rhodamine 6G for SERS.
We present a new slot-in type of optical correlator that is more compact than the previous types. The correlator can fit
inside the cabinet of commercial personal computers and is fully controllable with windows-based software. The
correlator is a Joint Transform type (JTC) and its optical system fits inside a metal box measuring 140 mm (W) x 220
mm (L) x 40 mm (H). The optical source is a 650-nm-band laser diode of the kind used in DVD systems. A spatial light
modulator and a CMOS camera are installed in the metal box with the passive optical components required for the JTC.
The collimated light from the laser diode is illuminated on the spatial light modulator displaying reference and data to be
examined. The light reflected from the modulator is Fourier-transformed by a lens on the plane of the CMOS camera.
The computer reads the power spectrum recorded by the camera and modulates the spatial light modulator. This process
is repeated. We found that these JTC processes could be performed with the prototype developed in this study.
A novel plasmonic Raman sensor using periodic nano-hole and, potentially, nanofocusing arrays is investigated
numerically and experimentally. The effect of structural parameters (such as periodicity of the structure, hole
dimensions, etc.) is determined and investigated. The analysed structures are fabricated in thin gold films by means of
focused ion beam lithography. Optical characteristics of the fabricated arrays are determined experimentally and
compared with the theoretical predictions. Experimental field enhancements are determined and also compared with the
theoretical predictions.
KEYWORDS: Near field optics, Modulation, Frequency modulation, Fermium, Semiconductor lasers, Near field, Silver, Silica, Amplitude modulation, Signal detection
The performances of a random-metal dielectric film composed of silver and fused silica balls were analyzed
experimentally under optical AM and FM signal transmission. Optical AM and FM signals emitted from a 1550-nm-band
laser diode were clearly transmitted in the random metal-dielectric film and through the optical near field generated
on the film. Based on these signal transmission results, the feasibility of using this film to transmit optical AM and FM
signals was experimentally confirmed in detail.
We propose a new technique for retrieving color information. The color data taken by a digital camera is transferred to
two-dimensional data on the color chart and displayed on a spatial light modulator. This modulation technique is
combined with a retrieval technique using a joint transform correlator. The color data, e.g., photograph of a flower, are
retrieved by this system, and the same color data (photograph) can be perfectly selected from the many reference data.
This technique will open a new area of retrieval techniques for ambiguous images based on shape and color information.
KEYWORDS: Near field optics, Silver, Dielectrics, Silica, Finite-difference time-domain method, Radio propagation, Absorption, Light wave propagation, Near field, Integrated optics
The propagation characteristics of a random-metal dielectric film acting as a propagating far-field light/optical near-field
converter were investigated. A finite-difference time-domain method was used for the analysis of the characteristics,
because of the complicated structure of the film formed with fused silica balls and silver paste. The propagating
efficiency of the optical intensity was estimated, and two efficiency-determining factors were clarified; the optical
coupling efficiency determined by the silica ball size, and the absorption determined by the silver layer between the
silica balls.
The operating characteristics of a novel optical near-field generator are described in detail. The generator was fabricated by forming a random metal-dielectric film composed of silver paste and spherical fused silica on the facet of a laser diode. The relationship between the current injected to the laser diode and the intensity of the optical near field is similar to that between the injected current and optical output power emitted from the opposite facet having no metal-dielectric film, although the magnitude of the optical intensity is very different. The threshold current and kink-points in the current-optical intensity relation show no difference in the both relationships. Lasing spectra observed in propagating light scattered from the optical near field corresponds to those of light emitted from the opposite facet. The direct current (DC) characteristics of the optical near field are similar to those of the propagating light emitted from the laser diode, and the linear relationship is maintained between DC characteristics of the optical near field and of the propagating light. The modulation characteristics of the optical near-field coincide with those of laser diodes because the intensity of the optical near field linearly responds to the magnitude of the injected current of the laser diode. These results confirm that the optical near-field generator is a practical optical source and will be important for future photonic devices such as OEICs.
An optical heterodyne alignment system used in an SR stepper, the SS-1, is capable of high resolution, but its practical accuracy is affected by multiple reflections between the mask and the wafer. These multiple reflections cause a significant phase modulation when there is an inclination error in the heterodyne optics. In order to attain high alignment accuracy, an opaque film coating and an anti-reflection coating have been applied to an X-ray mask. The multiple reflections between the mask alignment mark and the wafer surface can be reduced by coating chrome films on X-ray mask alignment mark area. The mask distortion of less than 30 nm (3 (sigma) ), caused by forming 500-angstroms thick chrome films on a chip is obtained in the measurement. As a result, an alignment accuracy of 23 nm (3 (sigma) ) is achieved by a double-exposure experiment with the X-ray mask.
The longitudinal mode hopping and the related terminal electrical noise in InGaAs/GaAs ridge single quantum well (SQW) lasers are investigated. It is found that electrical mode hopping has a Lorentzian dependence. The correlation with the optical noise is experimentally shown for low and medium frequencies.
Degradation modes and reliability in various types of semiconductor
lasers are reviewed in connection with the system application. Reliability and marked degradation modes of conventional DH type Fabry-Perot (FP) and distributed feedback (DFB)lasers are first clarified. Based on their degradation modes,new devices, such as highly coherent multiple-quantum-well (MQW)lasers and strained (M)QW lasers including pumping sources of Er3-doped fiber amplifier, are discussed from the viewpoint of the degradation modes and reliability.
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