In this paper, we introduce a floating plasmonic absorber having multiple resonances in the 8 ~ 14 μm spectral range and broadband absorption characteristics by adjusting Drude relaxation rate of metal. This plasmonic broadband resonator capable of capturing light with a large optical cross-section area is able to substantially enhance the performance of micro-bolometer (response time, noise equivalent temperature difference, pixel size and so on) due to the significantly reduced thermal mass and conductance. Firstly, to adjust Drude relaxation rate, the mean crystalline size of metal was optimized by changing the deposition condition and the absorption characteristics of absorber were measured by Fourier transform infrared spectroscopy in the 8 ~ 14 μm spectral range. The measurement results show that 1.62 times of broadening in bandwidth was obtained by decreasing the crystalline size from 5.73 nm to 3.18 nm while maintaining the maximum absorption at resonant wavelength of 10 μm within 93 ~ 95%. Comparisons between measurements and CST microwave studio simulations show similar spectral absorption trends. And then, to integrate plasmonic absorber with micro-bolometer, various kinds of plasmonic absorbers which have combinations of short and long dipole resonators were designed and simulated. Based on these results, 12 μm micro-bolometer pixels integrated with plasmonic broadband Ti absorber are designed and fabricated. The optimized Ti resonators with multiple resonance and small crystalline size absorb 88 % of the unpolarized radiation in the 8 ~ 14 μm spectral range on the average.
We propose a resonant optical Yagi-Uda nano-antenna fabricated at the end of the optical fiber probe for the sake of
extracting the information of the angular directivity by absorption of directional emission as a subwavelength optical
microscopy. A Yagi-Uda nano-antenna consists of a feed element surrounded by a reflector and three directors. The
reflector and directors are optimized in pitches with regards to resonance of the antenna elements using the finiteelement
method. We used a focused ion beam (FIB) to cut the end of the fiber probe tip away and make the flattened
surface to mount the metal nano-antenna structure, followed by FIB platinum deposition patterning for the nano-antenna.
To verify the characteristics of the probe based nano-antenna, directional emission from the metal slit with asymmetric
metallic surface gratings is probed and detected using the photomultiplier tube. Our approach of the nano-antenna based
fiber probe is suitable for scanning applications such as detection of directional emission.
We review recent advances in the plasmonic sensors associated with chemical and biological sensor system and
introduce their structural design method for enhancement of sensing performance such as detection limits, sensitivity,
and dynamic range, relative to the commercial systems. In addition, the effect of structural parameters of surface
plasmon resonance based sensors with transmission or reflection-type configuration is discussed. We also discuss the
optimal condition of the sensors with nano-structures as well as flat metallic layer structures for practical sensing and
provide the methods for improving sensing capability.
Proc. SPIE. 7757, Plasmonics: Metallic Nanostructures and Their Optical Properties VIII
KEYWORDS: Biosensing, Finite-difference time-domain method, Metals, Optical microscopy, 3D modeling, Near field scanning optical microscopy, Near field, Compact discs, Digital video discs, Optical storage
A double-layered nano-aperture on metallic film composed of a large square aperture under a small bow-tie aperture is
proposed. Numerical analysis of the proposed structure by using 3-dimensional finite difference time domain method
showed that the transmission enhancement factor reached about 245 at 20 nm away from the metal surface compared to
the incident intensity. Compared to the single-layered bow-tie aperture, the proposed structure had intensity about three
times higher than that of single-layered one at the same resonant wavelength of 1200 nm. In addition, a near-field full
width at half-maximum intensity spot size was about 56 nm in the <i>x</i>-direction and 64 nm in the <i>y</i>-direction. The
enhancement factor of the proposed structure was mainly depending on the size of the additional square aperture. These
properties can be adopted for nano-optical applications such as scanning near-field optical microscopy, optical data
storage, nano-lithography, and bio-sensing.
A numerical analysis of the fiber-optic surface plasmon resonance (SPR) sensor with crescent shape of metal coating is
presented. The crescent shape of metal coating usually occurs during one side metal deposition on the cylindrical fiber.
Here, for analysis of the performance of fiber-optic SPR sensors with such asymmetric metal coating, the method of
three-dimensional (3D) ray-tracing and theoretical calculation of electromagnetic reflection and transmission at the metal
film are applied simultaneously, which result in 3D analysis with reduced time consumption and data loads. We
investigate the characteristic of fiber-optic SPR sensor with asymmetric metal layer, comparing with those of the
symmetric metal coated fiber, and discuss the asymmetry effect of the sensors for practical sensing and provide the
information for improving sensing capability.
Fiber optic surface plasmon resonance sensor structure with double clad and subwavelength metallic grating is proposed.
The sensing characteristics of the proposed sensor structure are numerically analyzed with a combination of geometric
optics method and rigorous electromagnetic analysis method (rigorous coupled wave analysis). The analysis shows that,
in the proposed sensor structure, two resonance dips appear clearly. One has narrower bandwidth and the other has
higher sensitivity at resonance point shifted toward longer wavelength region in the transmission spectrum than the
conventional surface plasmon resonance sensor structure with flat dielectric/metal interface.
In this paper, we discussed the method for optimization of
fiber-optic surface plasmon resonance (SPR) sensor and the
effect of optimized parameters by analysis of the transmission spectrum of waveguide-based SPR sensors. Because of
their high sensitivity, the SPR sensors can be used in a lot of chemical and biological studies, but it is difficult to perform
a theoretical analysis of an SPR fiber sensor. Therefore, for the design and analysis of the sensor responses, a fiber-optic
SPR sensor can be optimized numerically by adjusting parameters such as the thickness of metal layers and the grating
period, etc. We simulated and optimized parameters by employing the method of the rigorous coupled wave analysis and
the genetic algorithm. Also we discussed the methods for improving sensing capability.
To enhance the functionality and flexibility of a multiwavelength fiber laser, characteristics such as the tunability of the lasing wavelength, the wavelength spacing and the number of channels should be investigated simultaneously. We have demonstrated a channel spacing and wavelength tunable multiwavelength fiber ring laser based on semiconductor optical amplifier and a novel tunable polarization-diversity loop configuration (PDLC)-based comb filter. The tunable PDLC-based comb filter would be composed of a polarization beam splitter and three wave plates (one quarter wave plate and two half wave plates) and a polarization differential delay line (DDL). Channel spacing can be controlled continuously by using a motorized polarization differential delay line. And wavelength can be simultaneously changed by controlling wave plates. The PDLC-based comb filter has the advantages of the input polarization independence and simple tunability. By employing the comb filter in the laser system, multiwavelength operation of up to 25 laser lines with the signal-to-noise ratio over 25 dB and 0.8 nm wavelength spacing has been demonstrated at room temperature. Also, we could achieve the increased output channel power of the laser while reducing the number of channels. The results show that the multiwavelength operation is even and stable. And we could achieve the output spectra of tuned wavebands with channel spacing of 1.6 nm and 0.4 nm when the semiconductor optical amplifier is driven with the injection current of 160 mA while adjusting a half-wave plate at each tuning set. As a result, the shift of lasing wavelength and wavelength spacing were continuously controllable in this system.